An unusual temperate ridge–cliff–talus system exists at Rock Rimmon in urban Manchester, New Hampshire. Recent surveys and historical data indicate that five natural communities occur within the system, of which three are critically imperiled in New Hampshire: Appalachian wooded talus, pitch pine–Appalachian oak–heath forest, and pitch pine rocky ridge. The remaining two natural communities are occasional in the state: Appalachian oak–pine rocky ridge and temperate acidic cliff. Seven plant taxa previously or currently recorded at Rock Rimmon are rare (SH, S1, or S2) in New Hampshire; four other taxa are uncommon (S3) in the state. We re-located two previously recorded rare taxa during our 2012 survey. Digitaria filiformis var. laeviglumis, a globally rare crabgrass, is endemic to this biodiversity hotspot, but was not re-located. In addition, four other rare plant taxa were not re-located, and all are likely extirpated as a result of the lengthy history of human-related disturbance at the site. The temperate ridge–cliff–talus system closely corresponds to NatureServe's central Appalachian pine–oak rocky woodland system, which is distributed from Maine to Virginia west to Kentucky and Ohio. Xerophytic oak and pine dominate across the range of this system type, although many canopy species differ along a latitudinal gradient.