Fifty-four years of ephemeral channel response to two years of intense World War II military activity, Camp Iron Mountain, Mojave Desert, California

During World War II, U.S. Army personnel lived, trained, and executed mock battles on low gradient piedmonts (∼2°) in the Mojave Desert. For example, Camp Iron Mountain (established in 1942 by General George S. Patton, Jr., and used until 1944) housed up to 20 000 Army personnel at any specific time. The camp is located on the large alluvial piedmont that extends from the Iron Mountains and is drained by shallow ephemeral channels. At this camp, we made 18 detailed topographic maps in order to compare drainage networks of six undisturbed control plots and 12 plots disturbed by army activities. There are significant differences between the morphometery of small-scale, ephemeral drainage networks on control plots, on plots bisected by stone-walled walkways, and on plots down gradient of former army roads. Control plot channels are wider (2.05 ± 1.48 m) and deeper (8.8 ± 4.5 cm) than channels in walkway plots (width: 1.19 ± 0.71 m, depth: 7.4 ± 4.1 cm) and in road plots (width: 1.18 ± 0.61 m, depth: 7.2 ± 6.7 cm). The military's modification of the landscape affected subsequent channel originations and orientations. Channel heads were found in 76% of the compacted and smoothed walkways. In walkway plots, 80% of walkways caused the orientation of channels to deviate from the steepest piedmont gradient by more than 20°. After more than 50 years, road berms still act as local drainage divides. Down gradient of each intact road berm, there is a wide (20-40 m) zone in which no channels exist. Where channels have developed below intact road berms, they are smaller than channels in undisturbed control plots. Down gradient of breached road berms, wide, braided channels are common. Fifty-four years after camp abandonment, the channel network at Camp Iron Mountain has yet to recover, primarily because rock alignments and road berms continue to influence drainage patterns and local gradients.