The purpose of this paper is to discuss briefly some factors of the hydrology in the Sierra Nevada foothills of the San Joaquin Basin. The data presented are primarily concerned with the hydrologic phases of a study started by the Forest Service at North Fork, California, in 1929 to determine the influence of the woodland‐chaparral vegetation on water‐yield, surface‐runoff, and erosion. [A complete discussion of the experimental results of the North Fork study is contained in a manuscript by P. B. Rowe, “influence of woodland‐chaparral vegetation on soil‐water relations,” submitted March 1940 for publication as a U.S. Dept. Agri