ber, 1936 1 mi. W summit Mt. Diablo, Contra Costa Co., Calif. Feb. 16, here are composed of decomposed sandstone and shale for the most part; a few agates of harder rock - though probably not igneous in nature - were visible. Vegetation present on this west facing slope included chiefly small annual grasses, but scattered about were Coulter Pine (P. coulteri), Ceanothus sp., Quercus chrysolepis, Baccharis. Mammal sign was abundant. Microtus & Citellus burrows and runways abounded. Two Neotoma fuscipes nests were found among boulders. Fecal pellets of Peromyscus, Neotoma, Microtus, Citellus were identified. Burrows seen, which were intermediate in size between those made by Microtus and those made by Citellus may have been constructed by Dipodomys; these burrows were abundant. One Citellus b. beeboyi was heard calling. Old Squirrel burrows were being used by smaller animals, for small holes were often found at or near the bottom of partially filled in squirrel burrows. I set out 48 mouse traps at approximately 10 paces spacing on this hillside. Found in traps this morning: 7 Peromyscus m. gambeli (5 discarded); 5 L. St. gilberti (2 discarded); 2 Microtus C. californicus; 4 Reithrodontomyx m. longicauda (1 discarded).