This study describes the composition and structure of a mature, second-growth Pinus taeda (Loblolly Pine) and Pinus echinata (Shortleaf Pine)-dominated old-field stand. Now owned by the University of Arkansas, this 22.5-ha parcel just outside of the city of Monticello, AR, has been protected as a de facto natural area since the 1950s. Many of the overstory pines exceeded 75 cm in diameter at breast height (DBH) and some have reached 100 cm. Increment cores indicated that most of the pine overstory originated between 80 and 100 years ago, probably following agricultural abandonment. Pine recruitment occurred somewhat gradually until the canopy closed, after which tree species establishment became dominated by hardwoods. Of the nearly 6000 tree seedlings/saplings per hectare in the interior of this stand, just under 4% were pine—the under- and midstory were dominated by shade-tolerant hardwoods. No obvious evidence of past land-management practices remained, save the rare old stump or formerly open-grown pine or oak. Coarse woody debris is beginning to accumulate in some portions of the stand, primarily from the senescence of short-lived hardwoods. Comparisons with other tracts in southern Arkansas suggest that this stand differs from other contemporary examples of mature pine-dominated timber, with a richness in composition and structure not apparent in managed stands of natural or planted origin.