March, 1904. Mammals of Southern California — Elliot. 273 



also, follows this stream to the desert." A short distance east of 

 the Pass is Warren's Well, where a few specimens were procured. 

 It is "in the Tree Yucca Belt, the upper edge of which is marked by 

 scrub-oak, juniper, and pihon pines. A considerable number of speci- 

 mens were captured in Morongo Pass, among which was a new 

 species of OuycJwmys and topotypes of Thomomys cabezoncs. The 

 next camp was made at Burn's Spring, in Burn's Canon, on the 

 east slope of the San Bernardino Range, at an altitude of 5,000 feet. 

 This "is situated in the Upper Sonoran Zone amid the pihon pines, 

 tree yuccas, junipers, and scrub-oaks. In this region the creosote 

 bush is found at an altitude of 4,500 feet and carries the Sonoran 

 Zone well up the canon. Above the canon are flats where cacti 

 and yuccas abound, and the only Upper Sonoran plant found is the 

 juniper. The new Onychomys was also taken at this place. A 

 number of the desert species were found here, and Citellus leucurus 

 and Dipodomys m. simiolus were common. 



The Mohave Desert was now reached and the next stopping-place 

 was Old Woman's Spring, "situated on the level sandy desert at an 

 altitude of 3,200 feet, at the east base of the San Bernardino Moun- 

 tains. The creosote bush is the predominant vegetation on the 

 sandy areas, with various species of Atriplcx in the dry lake beds. 

 The tree yuccas straggle down to this locality, which is their lower 

 limit. Cacti are rare at the spring." Passing through Victor on 

 the Santa Fe Railroad, where one night was passed and a few speci- 

 mens secured, the next camp was made at Oro Grande, about forty 

 miles northwest of Old Woman's Spring, where a week was given to 

 collecting. "Oro Grande is situated on the Mohave River at an 

 altitude of 2,600 feet, where the river cuts through a nearly level 

 mesa country of granite formation, which rises a few hundred feet 

 above its bed. The Mohave sinks a little east of Oro Grande, but 

 the water is usually permanent in its bed the year round at this point, 

 and this marks the limit of the paludose plants and such species of 

 mammals as have followed this vegetation down from the river's 

 source. The vegetation of the neighboring hills and mesa is wholly 

 desert in character, and consists of creosote bushes, Atriplcx, vuccas, 

 and a large variety of cacti, in which many of the desert animals 

 find shelter. In the river valley are cottonwoods, willows, Bacharis, 

 grasses, reeds, etc., and in the drier parts of the desert are willows 

 (Chilopsis), screw-pod mesquites, sage-brush, etc. The plains and 

 hills through which the river flows are all in the Lower Sonoran Zone, 

 and the vegetation of the river valley is a part of that Zone." A 

 considerable number of specimens were obtained during the sojourn 



