Vascular Flora of Adobe Valley and Surrounding Hills, Mono County, California

Adobe Valley and the Adobe Hills lie east of the Sierra Nevada in Mono County, California, and are within the Great Basin Floristic Province. The flora of Adobe Valley and the surrounding hills is influenced by the Great Basin Desert to the east, the Sierra Nevada to the west and the northern Mojave Desert to the south. Adobe Valley is surrounded by the Adobe Hills, Benton Range and GlassMountain region, creating a circular closed basin with many small tributaries feeding into it. This topography contributes to the creation of a rare wetland complex, including alkali meadows, marshes, and lakes at the base of the hills, which represent some of the more botanically interesting terrain in the region. Prior to this study, the wetland complex of Adobe Valley had not been systematically investigated with regard to its botanical diversity. The vegetation types associated with the wetland complex are listed as threatened by the California Natural Diversity Database and face a number of conservation concerns including water pumping, overgrazing, and possible wind energy development. A total of 1525 herbarium specimens were collected within the study area over 59 days in the field from 2016 to 2018. The vascular flora of the Adobe Valley and Hills includes 397 minimum-rank vascular plant taxa, representing 194 genera and 61 families. Six taxa are only known from historical collections, 21 taxa are non-native and 27 taxa have conservation status. The results of the inventory are presented here in an annotated checklist, along with descriptions of vegetation alliances.

line ecosystems that occur farther south in the Owens Valley have experienced more severe water pumping and diversion effects. A botanical study of Adobe Valley and Hills provides an ideal baseline of information to make comparisons with other wetlands in the region to better understand this ecosystem and promote management that will support sustainable groundwater extraction. Throughout the entire Great Basin Desert, lack of baseline vegetation data has made it difficult to assess the effects of groundwater pumping (Elmore et al. 2006;Pritchett and Manning 2009). This study also contributes towards a research need that has been outlined in the Management Plan for the RSLER (Ellsworth 2016), which states that it is in need of a floristic checklist.

Physical Setting
Location.-The study area is located in eastern California along the Nevada border in Mono County, between Mono Lake and Benton Station along the north side of State Route 120 (Fig. 1). Adobe Valley (Fig. 2) is an enclosed valley, surrounded by hill ranges on all sides. Beyond the adjacent hills, the study area is located between two large north-south mountain ranges, the White Mountains to the east and the Sierra Nevada to the west. The study site is 241 km 2 (93 sq mi; Fig. 1). The boundaries of this study were mostly political and human made. Due to the expansive hill ranges extending to the north and east, a geographic boundary was difficult to determine. State Route 120 serves as the southwest boundary of the site for 20.5 km (12.75 mi). The northeastern boundary is the California-Nevada border. The other boundaries are a power line road that lies just east of the ridgeline of the Benton Mountains to the southeast, and State Route 120 to the west and southwest, Dobie Meadows Road to the northwest, and a 4WD road that intersects Huntoon Creek at the Nevada border to the north. The boundary of the study site   was designed to center around the alkali meadows and marshes (Fig. 3, 4), but also includes upland habitats with pinyon and juniper woodlands and arid lowland habitats composed of sagebrush and rabbitbrush vegetation (Fig. 5). The Adobe Hills enclose Adobe Valley on the north-northeast side, and the highest point of these hills within the study area is 2444 m (8018 ft).
The study area incorporates portions of the Benton Range and the Adobe Hills but does not include the Glass Mountain Range, which was the subject of a botanical inventory conducted by Michael Honer (2001). Honer's study included the western portion of Adobe Valley to State Route 120, which forms the western border of this study and bisects the valley.
Hydrology.-Prior to 40 million years ago (MYA) the portion of California that is currently recognized as the Great Basin Desert was part of the Nevadaplano, an ancient plateau that drained westward into the Pacific (Millar and Woolfenden 2016). As the current topography of the Great Basin began to develop during a time of much volcanic activity, the landscape we see today began to form, creating closed basins and mountain ranges with no outlets to the Pacific Ocean (DeCourten 2003). Today, the name Great Basin refers to a large region characterized by the lack of an outlet to the ocean. Throughout eastern California and Nevada, snow melts off mountain ranges and drains locally into basins, often forming permanent or ephemeral lakes. The study site is an example of this physiographic pattern. Water from the surrounding mountain ranges including the Adobe Hills, Benton Range, and Glass Mountain Range flows into Adobe Valley creating an enclosed wetland complex. In addition to underground water movement, there are two aboveground creeks that run from Glass Mountain to the east side of the valley: Adobe Creek in the northern part of the valley and Black Canyon Creek in the southern part of the valley; however, Black Canyon Creek was not flowing throughout the duration of this study. Most of the water that drains from the Adobe Hills and Glass Mountain terminates in the low areas of Adobe Valley; however, some water instead travels underground and resurfaces in Fish Slough, 40 km (25 mi) to the south (Zdon et al. 2019).
Springs.-There are seven springs within the study area ( Fig. 1). Five springs are located along the eastern edge of Adobe Valley. From south to north they are Browner Spring, Michelle Spring, Antelope Spring and two springs at River Spring (Fig. 6). Some snowmelt from the nearby Glass Mountain Range runs aboveground by way of Adobe Creek; however, most of the water travels across the valley underground and resurfaces at these springs. The two remaining springs are located in the Adobe Hills and are named Pizona Spring and Upper Pizona Spring.
Lakes.-There are three ephemeral lakes (Adobe, Antelope and Lake McNamara) and one perennial lake (Black Lake) in the study area (Fig. 1). Black Lake contained water for the entirety of this study. The first year Black Lake was clear and deep blue in color; however, in the second year there was what appeared to be an increase in sedimentation and the color of the lake changed to tan or dark brown. Adobe Lake occurs at the northern end of the valley and was dry during the study, except for April-June 2017 when there was a small amount of water in the lowest sags of the lake. Antelope Lake (Fig. 3) is an ephemeral lake that filled in winter 2016-2017 and remained full for a few months throughout spring 2017, but was dry throughout 2018. Antelope Lake forms a salt flat when it is dry, as does the shoreline of Black Lake. Lake McNamara is located in the hills on the border between California and Nevada and was dry when it was surveyed in August 2017. Based on the condition of the lakebed and the vegetation present, it appeared to have been dry for an extended period of time.
Topography.-Elevation at the site ranges from 2012 m (6600 ft) on the valley floor to the highest point at 2445 m (8018 ft) in the Adobe Hills. The highest peaks in the study area are an unnamed high point in the Adobe Hills (2445 m), Trafton Peak (2383 m), and Antelope Mountain (2322 m) (Fig. 1). The highpoint of the Adobe Hills is unnamed on USGS topographic maps, but will be herein referred to as "Adobe Peak"; it is surrounded by hills of almost the same elevation and does not stand out as an isolated peak of prominence, as Trafton Peak and Antelope Mountain do.
The Benton Range has a ridge that runs 12 km (7.5 mi) north to south in the southern part of the study area. There are a few canyons that cut through the range, the deepest being a canyon that bisects through a series of large granite outcroppings near Benton Hot Springs. The Adobe Hills do not have a distinct crest, but rather are part of a more extensive rolling hill range that stretches to the east where it meets the Huntoon Range and continues to the north outside the study area into Nevada.
The east side of Adobe Valley is 60-90 m (200-300 ft) lower than the west side of the valley. This elevation difference allows the water that drains from Glass Mountain to pool at the low point of the valley, creating ephemeral and perennial wetland complexes including Antelope Lake, Adobe Lake and River Spring Lakes (Fig. 6). The ephemeral wetlands become dry in the summer and form salt flats and dry lake beds (Fig. 3).
Geology.-The granodiorite of the Benton Range is the oldest rock type within the study area and was formed around 210 MYA during the Triassic (Krauskopf and Bateman 1977). Within the study area, the Benton Range granite is exposed along the western slope and is dominated by pinyon-juniper woodland.
A later pulse of magma formed the granite of Casa Diablo Mountain during the Jurassic, 160 MYA (Krauskopf and Bateman 1977). This granite is found at the southern tip of the study area and has a unique botanical assemblage when compared with the rest of the study area (Fig. 7). The plants of the Casa Diablo granite are comprised of mixed shrubland and many herbs not found anywhere else in the area, including Cercocarpus ledifolius var. intermontanus (Rosaceae), Chamaebatiaria millefolium (Rosaceae), Heuchera rubescens (Saxifragaceae) and Holodiscus discolor (Rosaceae). This geologic feature is easy to identify from State Route 120 as it forms large weathering piles of boulders at the southwestern end of the study area. While the Benton Range granodiorite has phenocrysts, dark inclusions and variable coarseness, the granite of Casa Diablo is coarse and does not have potassium-feldspar phenocrysts.
The more recent exposed rock is of volcanic origin and covers much of the Adobe Hills; these rocks were formed during the Miocene when the valley experienced a series of rhyolitic explosions (Krauskopf and Bateman 1977;Fig. 9). This area is covered in rocks of dense material, more so than other areas dominated by pinyon-juniper woodland. It hosts some species not found elsewhere in the area including Calochortus bruneaunis (Liliaceae) and Salvia dorrii var. pilosa (Lamiaceae). This rock is not exposed in much of the study area and is instead overlain with andesite from an event ca. 22-16 MYA (Gilbert et al. 1968). These andesites are most abundant in the Upper Pizona area, where the rocks are noticeably more brown in color than in the surrounding areas.
Olivine basalt is the most recently formed layer of rock in the study area that was formed from volcanic explosions during the Pliocene. The majority of the exposed olivine basalt occurs in the Adobe Hills and is covered by pinyon-juniper woodland. Basalt scoria, intrusive rock and flows are identifiable because of their red coloring and piles of scoria (Krauskopf and Bateman 1977).
The surficial deposits that cover Adobe Valley formed in the Pleistocene and Holocene. The most recent volcanic explosion created the alluvial fan deposits in the valley referred to as Bishop Tuff that was created by the Long Valley Caldera, 760,000 years ago, and filled the valley (Krauskopf and Bateman 1977). An earlier volcanic episode deposited the pumice that is still exposed throughout much of the valley floor. Much of the soil of the entire study site, especially within the valley, is very well drained. This deep sand formed from volcanic ash and mixed alluvium. Sand dunes build up in the northeast section of the valley (Fig. 8), where westerly winds deposit airborne sand (NRCS 2018).

Climate
The Great Basin Desert is categorized as a "cold-desert shrubland" with a large temperature range between summer and winter (Lathrop and Rowlands 1983). Due to the rain shadow effect caused by the Sierra Nevada, precipitation reaching the study area from the west is relatively low. Storms on the west side of the Sierra Nevada often do not make it over the crest, and if they do, they warm as they descend over the eastern slope (Hidy and Klieforth 1990). There are different precipitation regimes throughout the year. In the winter, which is the wettest season, the Great Basin is influenced by Pacific cyclones. In the summer, warmer thunderstorms that come up from the Gulf of Mexico provide little precipitation (Hidy and Klieforth 1990). The closest weather station to the study area at Benton receives annually on average 19 cm (7.5 in.) of rain and 34.8 cm (13.7 in.) of snow (WRCC 2019), with the majority of the precipitation falling in December and January; however there are gaps in data collection from this station. Prior to this study, California re-ceived below-average precipitation for five consecutive years (2012)(2013)(2014)(2015)(2016). The rain year (October 2015-October 2016) prior to the onset of field work for this study provided above-average precipitation with 26.56 cm (10.46 in.; CDEC 2019). The timing and amount of precipitation caused prolific germination of many annual plant taxa which may have not been otherwise documented under drought conditions. The second field season in 2018 received below-average precipitation, 9.8 cm (3.85 in.), and the diversity of annual and herbaceous plant species was observed to be lower. The closest consistent snowfall data available is from the Lee Vining Weather Station, 35 miles from the study area, which reported 232 cm (91.5 in.) for 2016-2017, with the majority of snow in January andFebruary. For 2017-2018, 56.9 cm (22.5 in.) of snow was reported (NOAA 2019). Many plants in the mustard family (Brassicaceae), especially Thelypodium Endl. and Boechera A. Löve & D. Löve, were observed in 2018 because many are biennials and had germinated with the 2016 precipitation.
Temperature.-Temperature fluctuations between seasons increase and differences between daytime and nighttime temperatures also increase east of the Sierra Nevada crest. There is an extreme difference between winter and summer high and low temperatures (Hidy and Klieforth 1990). July is the hottest month of the year with an average high of 33.9°C (93°F) and December is the coldest month of the year with an average low of -9.4°C (15°F) as recorded by the Benton weather station (The Weather Channel 2019).
Wind.-Winds throughout the Great Basin Desert often play a large role in the geomorphology of the region as well as the development of sand dunes in basins (Hidy and Klieforth 1990;Fig. 8). Due to the location of the study area, with the Sierra Nevada to the west, many of the winds reaching the study area originate from the south and north and blow parallel to the Sierra Nevada (Zhong et al. 2008).

Paleo-Vegetation
The rain shadow effect and aridity of eastern California caused by the formation of the Sierra Nevada has had a significant effect on the current distribution of plant taxa in the study area (Axelrod and Raven 1985). The extant distribution of plant taxa is the result of a history of disturbances affecting climate, causing cycles of cooling and warming throughout geologic time (Millar and Woolfenden 2016). Taxon identifications based on pack rat middens have been used to understand past plant distributions in the eastern Sierra Nevada (Woolfenden 2003). During the Pleistocene, conifers throughout the Great Basin Desert existed at lower altitude than they do today (Millar and Woolfenden 2016). Within the study area, this applies to the juniper and pinyon belt, which occurs at elevations of ca. 2000 m in the modern era, but is thought to have occurred at lower elevations extending across basins that are now dominated by Ericameria nauseosa (Asteraceae) and Grayia spinosa (Chenopodiaceae). As climate warmed, Pinus monophylla (Pinaceae) and Juniperus osteosperma (Cupressaceae) receded to the range they are currently found (Millar and Woolfenden 2016).
A pollen core sampled from within the study area at Black Lake dates to the early Holocene. The majority of the plants identified in the core were Amaranthus L. (Amaranthaceae), Ambrosia L. (Asteraceae), Carex L. (Cyperaceae) and Pinus L. (Pinaceae), all lacking species identifications. The sampled pollen core coincides with the aridification and transition to the modern day halophytic flora of the region (Davis 1999). This early-Holocene transition is characterized by a transition from Juniperus (and other Cupressaceae throughout California) pollen fossils to an increase in percentages of Asteraceae, Chenopodiaceae and other halophytic taxa pollen fossils sampled in pack rat middens in the greater region, including Owens Lake and high-elevation lakes in the Sierra Nevada (Davis 1999).

Wildlife
There is very little development within the study area, aside from high voltage power lines that cut across the study site, and one major paved road (State Route 120) that bisects Adobe Valley. The surrounding region is also minimally developed, which creates continuous habitat for wildlife, including animal species that require a large uninterrupted range.
There is potential for Adobe Valley to serve as habitat for the Bi-State Distinct Population Segment of the greater sage grouse (Centrocercus urophasianus Bonaparte) although there are no active leks in the area. The Granite Mountain lek was historically located in Adobe Valley, but was determined to be inactive as of 2001. The Bi-State Action Plan (Bi-State Technical Advisory Committee Nevada and California 2012) identifies wild horses that occur in the study site, as a major threat to greater sage grouse. Other threats to greater sage grouse include livestock, pinyon-juniper woodland encroachment, and habitat conversion. Sage grouse avoid lekking and nesting in areas with Pinus monophylla and Juniperus osteosperma nearby (Casazza et al. 2011;Coastes et al. 2017) and prefer increased shrub cover (Kolada et al. 2009).
Wild horses (Equus caballus L.) are frequently seen in Adobe Valley (Fig. 10). In a 2015 survey, there were 314 adult horses and 40 foals counted (Ellsworth 2016). Over the course of this study, horses were often observed in the vicinity of River Spring during spring and summer. Smaller groups of horses were observed throughout the hills and around Adobe Lake.
Pronghorn (Antilocapra americana Ord) are often seen throughout the valley floor. There were three historical releases of pronghorn into the valley in the 1980s (Ellsworth 2016). Fences around River Spring are designed to discourage wild horses, though they typically jump over the fences, and encourage pronghorn, who can crawl under fences (Ellsworth 2016). There is a population of the Casa Diablo Herd of Rocky Mountain mule deer (Odocoileus hemionus Rafinesque) that seasonally use the hills south of the Pizona area. At River Spring, some notable wildlife include the naturally occurring Wong's springsnail (Pyrgulopsis wongi Hershler) and the introduced Amargosa pupfish (Cyprinodon nevadensis amargosae Miller). The last known Californian locality of Pygmy rabbits (Brachylagus idahoensis Merriam) is in loamy soils of sagebrush islands (stands of taller sagebrush within a dominant sagebrush landscape) around Mono Lake, including Adobe Valley (Larrucea and Brussard 2008).

Human History
Prior to 1900.-Although people are thought to have lived in Mono County for the past 10,000 years, permanent settlements are only known from the area for the past 1000 years (NRCS 2018). The indigenous people of the region are considered part of the Northern Paiute (Lawton et al. 1976). Paiute communities spanned the Owens Valley with the Sierra Nevada being the western edge of the area they occupied and Death Valley and Fish Lake Valley being the southern and eastern edges, respectively (Steward 1933). Important known food plants were Elymus cinereus (Poaceae), Elymus triticoides (Poaceae), and Stipa hymenoides (Poaceae), and the highly caloric Pinus monophylla (Pinaceae; Lawton et al. 1976). The Owens Valley was one of the most densely populated regions of the Great Basin Desert, with an estimated population of 6500 in the 1830s (Fowler and Beierle 2012). Ditch irrigation was used throughout communities south of the study area, but irrigation is not known from the Mono Lake area (Lawton et al. 1976). These irrigation systems enhanced native vegetation for consumption, but no crops were planted in the Owens Valley until after European settlement (Sauder 1990). Two important obsidian sources for arrowheads are found near the study area: Glass Mountain to the west and Truman Meadows to the east. The Benton Paiute Reservation, which is at the intersection of U.S. Route 6 and State Route 120, is 5 km (3 mi) east of the study site and currently has 138 members. Utu Utu Gwaitu, which means Hot Water Place people, is the Paiute name for the Benton Paiute.
In 1853, LeRoy Vining settled the west side of Mono Lake. Vining, along with other prospectors from this time, explored the eastern Sierra Nevada, Bodie Hills and Benton for potential mining. The Great Basin Desert as a whole was sparsely settled in the 1860s beyond the Mormon territories (Sauder 1990). As the gold rush west of the Sierran crest died down, the eastside mining towns of Aurora and Bodie began to take off. The study area was not historically mined, but it was used by ranchers beginning in the 1860s (NRCS 2018), predominantly for sheep and cattle grazing. George W. Parker was the first European settler to homestead in Adobe Valley. During this time, roads through the valley served to connect nearby towns. A historical stagecoach stop remains standing in the center of River Spring, along with associated horse corrals and irrigation ditches (Fig. 11, 12). One other remaining historical structure in the Adobe Hills is from a homestead called Pizona.
Human Impacts to the Region.-Between 1905 and 1930, the LADWP bought over a thousand farms and ranches throughout the Owens Valley and with it gained the water rights necessary to export water to Los Angeles (Libecap 2009). The first aqueduct was completed in 1913 and a second in 1970 to meet Los Angeles' increasing water needs. The second aqueduct diverted water from the Mono Basin and ran east of the study area. Beyond surface water, harvesting of groundwater was also needed to meet water export quotas, especially during the droughts of the late 1980s, when groundwater made up a significant percentage of the water diverted from the Owens Valley (Elmore et al. 2003). As of 2010, LADWP owns over 300,000 acres of land in Mono and Inyo County (LADWP 2010). There are two springs, Michelle Spring and Browner Spring (Fig. 1), within Adobe Valley that are owned by the LADWP; however, they are not exporting water from the springs at this time.
A portion of the study area is also used by ranchers. There are grazing allotments throughout the Black Lake Preserve, the historical Adobe Ranch and areas managed by the BLM. The INF permits horse packers that lead summer trips from Adobe Valley into the Adobe Hills near Pizona and beyond to Nevada. Seasonal encampments to support these trips were observed near Pizona. Benton Hot Springs, which is 5 km east of the study area, is the closest attraction that brings people to the area for camping and hot springs.
Land Management.-Most of the valley floor is managed by the BLM, except for the alkali meadows, seeps and springs, which are mostly private parcels. The Eastern Sierra Land Trust manages the Black Lake Preserve and the southern end of Adobe Valley. North of Black Lake are two parcels with unnamed springs that are owned by the LADWP. RSLER is at the center of the study area and is the largest wetland complex in the valley; it is managed by the CDFW. North of River Spring is the historical Adobe Ranch, which is privately owned and includes Adobe Lake. The entirety of the Pizona and Adobe hills are managed by INF. There is minimal development on lands managed by the National Forest other than historic structures; however, there is a power line and affiliated access road running northsouth through the hills. There is also a utility building on top of Antelope Mountain, including a geodetic GPS station, which measures movement between the Pacific and North American tectonic plates.
Conservation Concerns.-Off-road vehicle use is gaining popularity throughout eastern California. This activity was observed occasionally during fieldwork, throughout the BLM and INF lands, even in the most remote areas of the study site. Off-road vehicles' use can cause habitat degradation. In addition, construction and maintenance of roads can cause population fragmentation, alter drainage and waterways, introduce non-native species, and cause soil compaction (Fig. 13).
Other threats to vegetation include trampling, grazing and soil compaction from the extensive herd of wild horses present within the study area. Trampling and grazing damage appeared to be most concentrated in the meadows and marshes that remain inundated with water year round. People often drive off the highway onto dirt access roads, or hike out into the valley, to get closer to the wild horses, usually to take photographs. Cattle grazing within the study area has also led to compaction, particularly in riparian areas. Wind development has been proposed in the area, at sites near Benton and Sagehen Peak, but proposed projects have not moved forward since the most recent proposal in 2010. If water pumping were to take place in the valley, on the land already owned by the LADWP, it could alter the water table and have a significant impact on the alkali meadows and marshes.
Botanical History.-Prior to this study 105 herbarium specimens had been collected within the boundaries of the study area (Table 1, Fig. 14). These represent 85 minimum-rank taxa. Forty-eight of these collections were made from the vicinity of Black Lake, which is the closest lake to the highway.
Harvey Monroe Hall was the first botanist to collect in the study area (CCH 2019). He visited in 1912, the same year his Yosemite flora was published with Carlotta Case Hall. Hall studied Asteraceae and three of his four collections were in that family. Victor Duran visited the study area in 1927 and 1932, making four collections. However, he was known to collect upwards of 50 duplicates per collection (Lloyd and Mitchell 1973). Duran spent years studying the flora of the White Mountains and collected for the UC herbarium. Jim Reveal, expert in Eriogonum Michx., collected plant specimens in the study area in 1962-1963. Mary DeDecker, authority on the flora of the eastern Sierra Nevada and Owens Valley, collected Tetradymia tetrameres ( Fig. 15) from the sand dunes ( Mojave Desert (1984) and Mines of the Eastern Sierra (1993) and founded the Bristlecone Chapter of the California Native Plant Society (CNPS). The known occurrences of most of the sensitive taxa in the area were documented by Dean Taylor throughout his floristic work in Mono County (Taylor 1981;Keeler-Wolf 1990).
There are several published floristic inventories that have contributed to our understanding of the Great Basin Floristic Province of California. The nearby White Mountains, which are visible from Adobe Valley, were inventoried by Lloyd and Mitchell (1973) and expanded upon by James D. Morefield, Dean W. Taylor and Mary DeDecker (Morefield 1988;Morefield et al. 1988) and Phil Rundel (Rundel et al. 2008). Michael Honer published a flora of the Glass Mountain region (2001), which documented 489 taxa and included the western side of Adobe Valley. Other floristic inventories conducted in Mono County and east of the Sierra include the Bodie Hills (Messick 2019), the Sweetwater Mountains (Hunter and Johnson 1983) and the Upper Walker River (Lavin 1983).
methods Herbarium collection methods.-Prior to beginning fieldwork, a list of taxa known from the study area was compiled based on searches for herbarium specimens at the California Botanic Garden [formerly Rancho Santa Ana Botanic Garden] herbarium (RSA-POM) and on the Consortium of California Herbaria web database (CCH 2019). Permits were obtained from the BLM, INF, CDFW and LADWP to survey their lands and collect plants. Letters of permission were also obtained from the Adobe Ranch, the landowner of Antelope Lake and Black Lake Preserve. A total of 59 days were spent in the field with the majority of the field collecting taking place in the months of May, June and July in 2017 and 2018. Collection sites were planned based on phenology, with the explicit goal of surveying areas with few to no historical botanical collections and habitats identified as unique via satellite imagery and geologic maps, in order to document as many taxa as possible. Location, including longitude and latitude, elevation, plant abundance, associated taxa, vegetation type and habitat descriptions were recorded for every collection. Specimens were collected with diagnostic features including flower and/or fruit whenever possible.
Specimens were collected in triplicate whenever possible. All specimens have been deposited at California Botanic Garden RSA-POM, with duplicates deposited at University Herbarium at Berkeley UC-JEPS and Reno Herbarium RENO. The RSA-POM herbarium was used as a reference to help verify plant identifications, along with the Jepson eFlora (Jepson Flora Project 2019) and the Intermountain Flora (Cronquist et al. 1972(Cronquist et al. -2017. The classification follows the Jepson Flora Project (2019), except for Boraginales, which follows Luebert et al. (2016) and Cryptantha, which follows Hasenstab-Lehman et al. Vegetation.-A list of major vegetation types was compiled during the first collecting season. During the second field season vegetation plot data were collected from each of these vegetation types to inform vegetation descriptions (see Appendix 1). Data collected within each vegetation plot included percent species cover, life form percent cover, a complete list of plant taxa, aspect, elevation, latitude, longitude, shrub height, seral stage and disturbance level. These plots, combined with field observations and vegetation alliances previously described by Sawyer et al. (2009), were used to generate the vegetation descriptions in this flora. The plot center was chosen by ensuring the entirety of the plot occurred within a cohesive stand and did not occur within a transition between vegetation types. The plots have a 10-meter radius and most vegetation types were represented by two to three plots. These were not randomly placed, but chosen based on vegetation signatures visible from satellite imagery.

Floristic Provinces
Adobe Valley and the surrounding hills are within the Great Basin Floristic Province, which includes two sub-regions in Mono County: east of the Sierra Nevada and the White/Inyo Mountains (CCH 2019). The Great Basin Desert is characterized as a region that has no hydrologic outlet and is primarily dominated by Artemisia tridentata in the low-lying valleys. Ninetyseven percent of the taxa documented in this study have been associated with the Great Basin Floristic Province, based on their distributions in the Jepson eFlora (Jepson Flora Project 2019) and representation in herbarium collections (CCH 2019), the remaining 3% were associated with the Desert Floristic Province or California Floristic Province.
Fifty-seven percent of the taxa documented in this study, or 226 taxa, are also found in the Desert Floristic Province. The Great Basin Desert differs from the Mojave Desert by an increase in elevation, decrease in winter temperatures and increase in winter precipitation (Beatley 1975). Vegetatively, the boundary of the Mojave Desert and Great Basin Desert are characterized by the switch from creosote bush scrub to sagebrush steppe and pinyon-juniper vegetation (Jepson Flora Project 2019).
U.S. Route 395 is used in the Jepson Manual (Baldwin et al. 2012) as the boundary between the Sierra Nevada Region and the Great Basin Province. Sixty percent, or 236 taxa, documented in this study are categorized as Sierra Nevada taxa. Forty-eight minimum-rank taxa, or 12% of the flora, are considered widespread throughout California.

Vegetation
The distribution of plants and the assemblages they form is influenced by geology, water availability, aspect, temperature, elevation and soil type. The following section describes the main vegetation types found in the study area. In nature, plants often do not follow the descriptions provided by books, so the following descriptions are based on field observations, but are informed by the classification of Sawyer et al. (2009).

Woodlands
Pinyon-juniper woodland is the dominant vegetation found in the highest elevation belt of the study area. Within the Adobe Hills, Pinus monophylla is the dominant tree cover, while Juniperus osteosperma forms a less dense tree cover. Within the woodlands of the study area there are two main vegetation alliances: Pinus monophylla/Cercocarpus ledifolius-Artemisia tridentata-Purshia tridentata and Pinus monophylla-Juniperus osteosperma/Artemisia tridentata (Sawyer et al. 2009).
MIXED SHRUB/WOODLAND: Pinus monophylla/Cercocarpus ledifolius-Artemisia tridentata-Purshia tridentata.-This vegetation alliance is found on the granitic outcrops of the Benton Range (Fig. 7). It often occurs among large boulders and hosts many rock-dwelling plant species. Although usually containing less than 20% shrub cover, it has the greatest diversity of shrubs of all the vegetation types. This vegetation type covers less the 1% of the study area, but supports 30% of the floristic diversity (118 taxa). In addition, 66 taxa (17% of the flora) documented in the study area were endemic to this vegetation type. This is the highest diversity and endemism of any vegetation type documented in the study.  Fig. 5). It also comprises the dominant vegetation in the basins of the Adobe and Pizona hills. This vegetation type occurs in deep alluvium, and there is very little diversity in shrub taxa. The observed difference in annual herb diversity between 2017, which received above-average precipitation, and 2018, which received belowaverage precipitation, was greater than any other vegetation type. There were 75 taxa (19% of the flora) documented from this vegetation type and 22 taxa (6% of the flora) that were only found at this vegetation type. Although widespread, there are many conservation concerns facing the sagebrush steppe including: pinyon-juniper encroachment, wildfires, and impact from non-native plants (Schindler 2011 This is an early seral vegetation type that often has a dense canopy. There are fewer annual herbs in this vegetation alliance than are found in other shrubland assemblages, but there is more abundance of non-native grasses due to the disturbance level and proximity to the roads. This vegetation type covers 8.4% of the study area. There were 15 taxa (4% of the flora) documented from this vegetation type and three taxa that were only found in this vegetation type. TREES AND SHRUBS: Artemisia tridentata, Atriplex  SAND DUNE HORSEBRUSH SHRUBLAND: Tetradymia tetrameres.-This vegetation type is only represented in the northeast corner of Adobe Valley, where westerly winds carry and deposit sands to create vegetated and non-moving sand dunes and interspersed through the sandiest basins of the Adobe Hills (Fig. 8). Although this vegetation type is not widespread, it is included here because the dominant species is rare to California. The sand is very deep and the canopy cover is sparse. Total vegetation cover is less than found anywhere else in the study area, except for exposed salt flats of ephemeral lakes during summer months. This vegetation type covers 2.1% of the study area. There were 17 taxa (4% of the flora) documented from this vegetation type and four taxa that were only found in this vegetation type. TREES AND SHRUBS: Chrysothamnus viscidiflorus, Eriogonum

Riparian Vegetation Types
The riparian vegetation types are dependent on either springs, lakes or creeks and the taxa found there are dictated by whether water is seasonal or permanent. There are two year-round creeks, Adobe Creek and Pizona Creek, that harbor montane riparian scrub-dominated riparian belts along the creek shores. River Spring is the largest spring and emergent freshwater marsh dominated by Schoenoplectus acutus. As water moves from the source of the springs and through the very alkaline soils of the study area it quickly becomes an alkaline marsh, dominated by Iris missouriensis and Carex spp. The water table lowers moving farther from the springs and the dried alkali meadows begin. These also line the shores of the lakes of Adobe Valley.
GREAT  Fig. 3). Since groundwater pumping began throughout eastern California, this habitat type has been in decline. The herbs and grasses are similar to the Sarcobatus shrublands but these are meadows and have no shrub canopy. They are located along the toe slope of the Adobe Hills and Benton Range, where water pools in the winter and dries out in the summer. This vegetation type covers 3.5% of the study area and 37 taxa (9%) were documented from this vegetation type, but only six were only found here; many taxa found in alkali meadows were also documented in alkali shrublands.    (Fig. 4). These marshes have alkaline soil, which provides for alkaline wetland endemic taxa. -This vegetation type is only found surrounding River Spring and is valuable to note because it has more water and fewer alkali-specialist taxa than the alkali marshes (Fig. 6). The stands of Schoenoplectus are mostly monotypic and halfsubmerged in water, with Ericameria and grasslands on shore. This vegetation type covers 0.005% of the study area. Twentythree taxa (6%) were documented at River Spring, of which fifteen (4%) were not found elsewhere.
There were only 85 minimum-rank taxa documented from the study area prior to this study, thus 312 minimum-rank taxa were documented for the first time as part of this study. There are 12 taxa known historically from within the study area that were not rediscovered. This study additionally documented 76 minimumrank taxa that were not known in the broader region when compared to the checklist for the Glass Mountain Region (Honer 2001) and historical collections made in the surrounding area in Benton and at Benton Hot Springs.

Sensitive Taxa
Astragalus johannis-howellii (Fig. 16) is the only plant documented in this study that is listed by the California Endangered Species Act as Rare (CR), which means it has an extremely high risk of extinction in the wild (CDFW 2020).
No taxa included are listed federally. The CNPS Rare Plant Rankings (CNPS 2018b) are used in this study to quantify rarity. The ranks that have been assigned to sensitive taxa within the study area are 1B, 2B and 4. Plants with a rare plant rank of 1B are considered rare throughout their range and often endemic to California. Plants with a rare plant rank of 2B are considered rare in California but are more common elsewhere. Plants of a rank of 4 are of limited distribution in California. The number that follows the rare plant rank is a threat assessment rating on a scale of one to three, with one being taxa facing severe or immediate threats to over 80 percent of their populations and three having a low degree of threats (less than 20% of their populations face immediate threats; CNPS 2018a).
There are 27 taxa included in this study that have conservation status (Table 3), six of which are shown in Fig.  15-20. One species of conservation concern was not rediscovered during the study: Goodmania luteola (Polygonaceae), documented by Dean Taylor near River Spring in 1998 (JEPS96605, Taylor 16730). Nine taxa of conservation concern were newly documented from within the study area: Astragalus oophorus var. oophorus (Fabaceae), Boechera cobrensis (Brassicaceae), B. dispar (Brassicaceae), Eremothera boothii subsp. boothii (Onagraceae), E. boothii subsp. intermedia (Onagraceae), Eriastrum sparsiflorum (Polemoniaceae), Micromonolepis pusilla (Chenopodiaceae), Thelypodium integrifolium subsp. complanatum (Brassicaceae) and T. milleflorum (Brassicaceae). Boechera cobrensis, B. dispar and Thelypodium integrifolium subsp. complanatum have previously been documented in Queen Valley, just east across the border in Nevada. Astragalus oophorus var. oophorus and Eriastrum sparsiflorum have also been collected in the nearby foothills of the White Mountains. Micromonolepis pusilla was previously known just outside the study area from Benton Station. Thelypodium milleflorum has been collected within the Adobe Hills, but just north of the study area. Eremothera boothii subsp. boothii is known from the south end of Adobe Valley, but outside the study area. Eremothera boothii subsp. intermedia is known from the southern Mono Basin and Mono Mills.
Rare taxa that were not documented but have potential to occur in the area include Mentzelia monoensis (Loasaceae), Phacelia gymnoclada and P. inyoensis (Hydrophyllaceae). Mentzelia monoensis was recently described as a cryptic species in Mentzelia sect. Trachyphytum from the Mono Basin, only 20 km west of the study area. Mentzelia albicaulis and M. montana are both morphologically similar to M. monoensis and are both commonly seen throughout the study area. Mentzelia monoensis is thought to be edaphically restricted to silica-rich rhyolite tephra of the Mono Craters, and this substrate does not occur within the study site (Brokaw et al. 2015). Phacelia gymnoclada was collected in 2011 by Jim André (UCR236144, André 18468) only three kilometers south of the southeastern corner of the study area, near Truman Canyon. Phacelia gymnoclada has been collected in adjacent regions of Nevada and is likely to occur within the study area. Phacelia inyoensis has also been collected southwest of the study area in the Benton Crossing area and is affiliated with alkaline meadows.
Only two species in the study area are endemic to California: Plagiobothrys parishii (Fig. 17) and Calochortus excavatus (Fig. 18). Two other species restricted to California and Nevada, but with limited distributions, are Astragalus johannishowellii (Fig. 16) and Boechera bodiensis. Astragalus johannis-howellii is restricted to Mono County within California; one population was found in the Adobe Hills, north of Adobe Lake; however, most known locations are from the vicinity of Long Valley, southwest of the study area (CNPS 2018a). In Nevada, A. johannis-howellii is known from Mineral County. Boechera bodiensis is known from Mono and Inyo counties in California and also occurs in Mineral County, Nevada. There are 22 known extant occurrences of B. bodiensis according to Nature-Serve (2018).
Calochortus excavatus and Plagiobothrys parishii both have ranges that extend from Lone Pine to the Bodie Hills area through the Owens Valley, with the study area being close to the northern extent of their distributions. Although this is a relatively large geographic range, most of their habitat is owned and managed by LADWP, which owns much of the alkali marsh habitat of the Owens Valley.
Calochortus excavatus (Fig. 18) is a halophytic perennial geophyte that is associated with alkaline soils that are perennially moist. This species is generally restricted to alkaline meadows and marshes of Inyo and Mono counties, and is usually found within the shadscale scrub plant community dominated by Atriplex confertifolia (Sawyer et al. 2009), although within the study area it was documented to be co-occurring with Ericameria nauseosa. Shadscale scrub is widespread throughout the Owens Valley, but the alkali meadows with perennial water found within the shadscale scrub are decreasing rapidly due to both drought and groundwater pumping. Alkali meadows were once common throughout the Owens Valley and are now considered "very threatened" as a community type (CNPS Bristlecone Chapter 2018). CNPS has ranked C. excavatus as a 1B.1, which means it is rare and severely threatened in California (CNPS 2018a). Globally C. excavatus is ranked as G2 (imperiled) and has a state rank of S2 (imperiled; NatureServe 2018). It is identified as a Species of Conservation Concern for both the National Forest and the BLM. Other than monitoring related to Habitat Conservation Plans and Environmental Impact Statements, which have not been continuous, there has been little systematic demographic data collection and no conservation plans implemented for C. excavatus.
Plagiobothrys parishii (Fig. 17) is also ranked 1B.1 by CNPS (2018a) and globally ranked G1 (critically imperiled) and state ranked S1 (critically imperiled), with only 14 extant occurrences (NatureServe 2018). The major threat facing P. parishii is water pumping, and half of the occurrences are on LADWP property throughout the Owens Valley and half of these occurrences have not been documented in over 20 years, according to the California Natural Diversity Database (2017). Plagiobothrys parishii has a disjunct population that has been documented multiple times in the Lucerne Valley of the Mojave desert as well.

Non-Native Taxa
A total of 21 non-native taxa were found throughout this fieldwork, 13 of which had not been documented from the study area. The majority of the non-native taxa are found in riparian areas (Table 4). These areas are the most utilized of the valley and hills and have the easiest road access. The only areas within the sagebrush scrub and pinyon-juniper uplands that have nonnative taxa are along roads. The exception to this is Bromus tectorum, which is found throughout the study area, although it is never a dominant groundcover anywhere.

Noteworthy Discoveries
An undescribed subspecies of Aphyllon californicum (Fig. 19) was collected along River Spring Road, one half kilometer northeast of the main spring at the center of River Spring Lakes. Previous collections from this population were determined as Orobanche ludoviciana and O. californica var. parishii. These collections key to Aphyllon californicum subsp. feudgei (Schneider and Colwell 2017) in the Jepson Flora Project (2019), which notes that plants of this taxon growing on Chrysothamnus are an undescribed subspecies. Host associations have been shown to be a driver for cryptic species diversification (Schneider et al. 2016), so it is important to note this population is parasitizing Ericameria nauseosa var. oreophila.
Nemacladus rigidus is another taxon that warrants further investigation into its range and abundance in California. It was found once during this study, on an east-facing slope of the Benton Range. Although there are many collections from Nevada, there are only a few collections from California. It is a small, easily overlooked annual plant that could potentially be more abundant than is reflected in its current known distribution. However, if it is not more abundant, then it should be considered for conservation status in California and should be evaluated by CNPS.
A collection by Mary DeDecker of Eriogonum heermannii var. humilius (DeDecker 6158, RSA626561) was the only taxon omitted from this inventory. It was verified to be correctly identified, but seems highly unlikely that this plant would occur in the study area, so it is assumed to be a location error on the label.

Annotated Checklist
The following annotated checklist (Appendix 2) represents taxa documented within the study area and is based on fieldwork I conducted in 2016-2018, including a review of historical herbarium specimens. All vouchers collected during this study have been deposited at California Botanic Garden RSA-POM. If a historical specimen is cited and that taxon was not relocated during the study, the herbarium where the specimen is housed is indicated if not RSA-POM. The classification follows the order classification of Angiosperm Phylogeny Group IV (Stevens 2001 onwards), familial classification of Jepson eFlora (Jepson Flora Project 2019), other than Boraginaceae, for which an updated treatment was utilized (Luebert et al. 2016) and Cryptantha which follows Hasenstab-Lehman (2012). Non-native taxa are designated by an asterisk (*), CNPS-listed rare taxa are shown with a dagger ( †) and taxa previously found but not relocated during this study are indicated with a diamond (♦).
Scientific name, common name and life form are provided for each taxon. Abundance is noted by the following terms: rare, uncommon, occasional, locally common, common and dominant. Taxa were categorized as rare if they were only found once. Uncommon taxa refer to plants with more than one population throughout the study area, but with a limited distribution. Occasional refers to taxa that have a wider distribution than the uncommon taxa, but are still infrequently seen. Locally common refers to taxa that are common in certain vegetation types.