JESimpson,1938 51. 925±ft, 1 mi. e. Caborca, Sonora April 15, 1938, continued. Señor Delgadillo watched camp, I crossed the Rio Altar (almost dry except for irrigation canals) to: 1100± ft., Cerro Cañeda, 2 mi. e. Caborca, Sonora. April 15, 1938, continued. Here on the steep, west-facing slope in rocks among palo verde, creosote, saguaro, nopal, and others set 60 mouse-traps and 7 rat-traps. April 16, 1938 Caught 4 Perognathus intermedius (♂171,172,173; ♀174), 6 Peromyscus eremicus (♂175, 176,177,178; ♀ 179,180:no emb), and 2 Neotoma albigula (♂ 181, ♀182: no emb). Shot a ground-squirrel high up in the large rocks (♀183:no emb) and two lizards, 184 in sand and 185 on mesquite branch. April 17, 1938 The mesquite dominating the area is different from most localities of occurence so far visited in that is very dense and very green in foliage. Much more water is available to it here (camp only 300-400 yards from river bank) near the Rio Altar, and the adjacent area is cut by many irrigation canals. After much repairing and miscellaneous camp-chores broke camp and drove toward Puerto de Lobos; camped at: 900± ft., 1.6 mi. sw Las Alesnas, 20 mi. wsw Caborca, Sonora. Set 50 mousetraps in the sand among creosote;