In 2003 to 2008, we conducted surveys to document the eastern and northern range limits of Red Tree Voles (Arborimus longicaudus) in the Columbia River Gorge and Hood River basin, Oregon. Our survey indicated the current range of the vole includes the area from Wahkeena Creek, 20 km east of Troutdale to Seneca Fouts State Park, 6 km west of Hood River. We also found a concentration of Red Tree Vole nests in the headwaters of the Lake Branch of Hood River, 27 km southwest of the town of Hood River. Of 70 vole nests located, 36 (52%) were old unoccupied nests with no evidence of recent use, 24 (34%) were unoccupied but had evidence of recent use as indicated by the presence of fresh green resin ducts or cuttings in the nest, and 10 (14%) were occupied by voles. Of the 70 vole nests, 74% were in forests dominated by mature or old-growth trees and 26% were in stands 25- to 60-y-old. This survey is the first to document the existence of Red Tree Voles in the upper Columbia River Gorge east of Cascade Locks. It also documents the occurrence of Red Tree Voles on the east slope of the Cascade Range in the headwaters of the Lake Branch of Hood River.