|Oregon Caves National Monument consists of 480 acres and lies deep within the Siskiyou Mountains of southwest Oregon. Complex geology, steep topography, and a diverse flora are characteristic of the monument and adjacent national forest land. The monument is drained by Cave Creek and two of its tributaries (No Name Creek and Panther Creek), with the main stream flowing through the cave and emerges at the main entrance, around which the developed area of the monument was planned. Keystone tree species found in this vicinity and along trails include mature Douglas fir, young white fir, Port Orford cedar, sugar pine, Pacific madrone, and big leaf maple. Elevation, aspect, and rock type account for most of the differences in vegetation at the monument, which contains some 400 different plant species. The purpose of this amended nomination is to extend the boundary of the original Oregon Caves Historic District, listed in 1992, to include much of the monument’s trail system. The four trails proposed for inclusion in the Oregon Caves Historic District boundary effectively create three loops: the Big Tree Loop, the Cliff Nature Trail Loop, and the No Name Loop, that collectively cover approximately 5.6 linear miles of terrain and range in elevation from 3,680 feet to 5,280 feet. In addition, there are two nominated sections of the system that are spurs on the Big Tree Loop, so the nominated system total is 6.7 miles. These trails feature rustic design principles consistent with National Park Service (NPS) standards of the 1930s and include character-defining features such as earthen tread ranging in width from 2 ½ to 4 feet, average vertical clearance of 10 feet, varied gradient ranging from 2 to 16 percent, sweeping curves, slope treatments such as rounding, as well as some original stone features including steps, recessed benches, and retaining walls. Only minor alterations have been made along the loops and the two spurs since 1941.