66 PROCEEDINGS OF THE CALIFORNIA 



west of the valley as far as known, except the Picus, v,-hich reaches the coast 

 mouutains in small numbers. 



REPTILES. 

 \. Platijtiiyra flavescens Agass., Yellowish Mud Turtle. 



2. Sceloporus vmghter 7 Hallow., Great Fence Lizard. 



3. Crotalus atrox Baird & Grd., Fierce Rattle Snake. ' 



4. Crotalus tigris Kexnic, Tiger Rattle Snake. 



5. C/iionactis occipitalis Hallow.. Banded Snake. 



6. Salvadora Grahamii Baird & Grd., Graham's Snake. 



7. P/tunpkis bellona Baird & Grd., Bellona Bull Snake. 



And probably others are limited by this valley if not peculiar to it. 



BATllACHIA. 



1. Bufo alvarius Girard, Colorado Toad. 



2. Bufo Woodliousii Girard, Woodhouse's Toad. 



I collected in this valley, while stationed at Ft. Mojave as surgeon, lat. 3.5°, 

 from Dec. 20th, 1860, to May 28th, 1801. During that time there was very little 

 rain, some frost and thin ice, severe winds from north and south, blowing the 

 sand and dust for days together, and in April some exceedingly hot weather, 

 the thermometer rising to 116^ in the shade. Accordijig to the observations 

 of those who have observed the climate in summer, thgre are then occasional 

 violent thunder storms. The whole amount of rain is, however, very small 

 throughout the valley, decreasing towards Ft. Yuma to about 2 inches annual- 

 ly, or less. The heat also increases, and there are several subtropical animals 

 foanid there which I did not meet with. Only three or four species of fish are 

 known to inhabit this part of the river. 



In going there in December, and returning in May-June, I spent 20 days in 

 the region next to be described. 



II. Desert Region. 



The region bordering this valley on the west may be called the Desert, most 

 of it being destitute of trees, and much of it without any vegetation whatever. 

 Its widtli at the southern boundary is 7.o miles, and a large tract is believed to 

 have been recently a shallow arm of the Gulf of California, rendered dry by 

 evaporation, and yet as much as 70 feet below the level of the sea. Beds of 

 salt, drifting sand, and sterile flats characterize this portion for a distance of 50 

 miles north. Beyond this point ranges of mountains occur, rising from 1,000 

 to .5,000 feet, and the intervening country is generally undulating. Vegetation 

 increases in a direct ratio to the elevation, the lowest parts generally consisting 

 of salt or alkaline flats, sand hills or bare rocks, while on the highest summits 

 there is a little herbage and small trees, chiefly Pinus monopliyllus and Junip- 

 erus occirhntalis. On some of the intermediate slopes there are groves of Yuc- 

 ca baccata, various shrubs and Cacti, other desert plants, and, towards the 

 south-west portion, some palms, lielieved to be the Brahea dulcis. Such oases 

 are inhabited by a few birds and other animals from the neighboring regions. 

 Towards the north the elevation and number of mountains increases, but the 



