Sierra Army Depot is a United States Army post located near the unincorporated city of Herlong, California 55 miles northwest of Reno, Nevada and 40 miles southeast of Susanville, California. Sierra Army Depot is in the highest desert plain east of the Sierra Nevada Mountains at an elevation of 4,200 feet. The high desert plain is only sparsely developed.
The terrain is flat or gently rolling, dominated by sagebrush. The Honey Lake Valley is immediately east of the Sierra Nevada mountain range. The mountains form a barrier to storm systems moving eastward from the Pacific.
Located in the rain shadow of the mountain range, the valley climate is arid, with low relative humidity and precipitation. Annual precipitation is low, averaging 5.6 inches. Temperatures remain moderate in summer and winter.