MAMMALS OF THE MEXICAN BOUNDARY. 



125 



CyVmclropuntki)^ Nicotiana, Xanthii/ni, and Baccharis (several spe- 

 cies), besides the following: 



Datura metf'JoUlcs de Candolle. 

 Viicurbita polmata Watson. 

 Aster spinosus Bentham. 

 Pluchca sericea (Nuttall) Coville. 



Scirpiis Occident alls (Watson) Cbase. 

 Scirpus oliieyi Gray. 

 Govillea tridentata (de Candolle) Vail.a 

 Foiiqiiieria sijleiidciis Engelniann. 

 Eckinocactus lecontei Engelmann. 

 PhiliberteUa cynanchoidcs (Decaisne) 

 Vail. 



No species of Agave^ Yucca, Nolina., or Basyliron was found here 

 or to the westward until the Coast Range was reached. 



Reftiles. — At Gila City we obtained a beautiful snake, Ophiholus 

 getulus hoylii (Baird and Girard), a mud turtle, Kinosternon sono- 

 riense Le Conte, and three species of lizards: Crotaphytus unslizenli 

 Baird and Girard, Uta symTnetrica Baird, and Uta graciosa (Hallo- 

 well). 



A few frogs {Rana) were seen, and fishes were abundant in the 

 Gila River. 



Station No. 67.— Yuma, Arizona. This station is on the left 

 (east) bank of the Colorado River, at the mouth of the Gila. The 

 channels of the Gila and Colorado rivers are marked by lines of tall 

 cottonwoods and a lesser fringe of willows. The adjacent bottom 

 lands, wdiich are broad and subject to annual overflow from the river, 

 are more or less covered with mistletoe-matted mesquites and screw- 

 beans. There are but few cacti, and these only in the hilly coun- 

 try in the vicinity of Yuma, where the creosote bush and desert wil- 

 low also grow. There are a few tall Mexican elders where the soil is 

 alluvial ; but the commonest shrubs of the low ground are the arrow- 

 wood and Baccharis. As a result of an investigation along the Colo- 

 rado River, made in January, 1902, by the hydrographic branch of 

 the U. S. Geological Survey, the extent of the alluvial bottom land 

 between Camp Mohave and Yuma was found to be from 400,000 to 

 500,000 acres. The alluvial deposits extend in a widening band 

 along the Colorado from Yuma to the Mexican Gulf of California, 

 forming a troj^ical tract which possesses distinctive biologic features. 

 Although the rainfall at Yuma is but 3.0(5 inches a year, this tract 

 is irrigable, and, like the Nile Valley, subject to annual overflowing. 

 These high waters are rich in fertilizing sediments, are exceptionally 

 free from alkaline salts, and come at an opportune time for irriga- 

 tion. At the time of our visit a Norwegian engineer was engaged 



a The creosote bush is abundant, extending to the Colorado River and down 

 that stream to its mouth at the Gulf of California. On the rich soil of the 

 lower Gila the finest specimens of cresote bush were seen, measuring almost 

 4 meters (13 feet) in height. 



