JESimpson, 1958 29. 1000 ± ft., 2 mi. n.e. Tinajas de los Papagos, Sierra del Pincate, Sonora March 24, 1938, continued the palos verdes, mesquite, and iron-wood of the wash contrasts with the adjacent lava fields. Here two miles to the northeast the creosote entirely dominates the cinder fields; near Papago tanks, however, creosote tho heavy is associated with some saquero, much ochotillo, cholla, palo verde, mesquite, etc. After putting up our specimens (Dr. Benson helped me.) we broke camp, and drove (accompanied by Mr. Lenon and his Plymouth coupe) six and a half miles to: 850 ft., Paso McDougal, Pinacate Region, Sonora Here we made camp at base of Sierra Hornaday. Set out 50 mousetraps along the face of " " ; 37 mousetraps in sand-grass at base of " " ; 50 live traps after dark within few hundred yards" ". March 25, 1958 Along the east face of Sierra Hornaday caught 9 Peromyscus eremicus (5♂+4♀; put up two: 69♀,70♂);. 2 Peromyscus crinitus (71♂and 75♀), and one Perognathus intermedius (but its skull was badly broken; also the tail of one was in a trap). In the sand and grass caught 15 Dipodomys merriami (100♂+5♀; see 730and 740) and one Perognathus pencillatus (720). Cheek-pouch contents of latter and the kangaroo rats saved. Sierra Hornaday, unlike the majority of the peaks and ranges of the near vicinity?, is not lava at all; it is composed of mazonite and granite mostly (granite-like but without quartz)