GEOLOGICAL SKETCH OF THE REGION OF TUCSON. 45 
position and transportation, with reference to the deserts of Texas, Chi- 
huahua, New Mexico, California, and Sonora. The city has a population 
of nearly 22,000. It is situated on one transcontinental railway, and has 
good connections with others, as well as shorter lines to various regions 
of interest. 
The business of the city and the conduct of its municipal affairs are 
largely in the hands of progressive Americans. The elevation of Tucson 
is 2,390 feet, while the highest of the mountains that surround the plain 
in which the city lies, the Santa Catalina Range, reaches about 7,000 feet 
higher. The University of Arizona, with its School of Mines, and the 
Arizona Agricultural Experiment Station are located at Tucson. 
Not the least of the advantages of Tucson as a center for the activities 
of the Laboratory is the broadminded comprehension of the importance 
of the purposes of the institution evinced by the citizens, accompanied by 
an earnest desire to codperate in its establishment. This appreciation 
was expressed in the practical form of subsidies of land for the site of the 
building and to serve as a preserve for desert vegetation, the installation 
and construction of telephone, light, and power connections, and of a road 
to the site of the Laboratory, about 2 miles from Tucson. The monetary 
value of these concessions is by no means small, and is much enhanced by 
the generous spirit in which they were tendered. This spirit of hearty 
cooperation has animated every organization in the city, and has enabled 
the Laboratory to gain control of a domain of 860 acres, of the greatest 
usefulness for general experimental work (plate 48). 
GEOLOGICAL SKETCH OF THE REGION OF TUCSON, ARIZONA.* 
PHYSIOGRAPHY AND GEOLOGY. 
The valley of the ancient Pueblo of Tucson, in Pima County, Arizona, 
is an expanded portion of the valley of the Santa Cruz River. This stream 
has great historic interest as one of the most direct routes by which the 
early Spanish explorers made their way from Mexico into the then 
unknown regions of the north. At Tucson the river occupies the western 
side of the valley at the eastern base of the Tucson Mountains, and flows 
northward toward the Gila River, but sinks in the sand before reaching it. 
In seasons of little rain it is an insignificant stream, but is subject to 
great floods in the rainy seasons, which sweep away acres of rich alluvions 
and change the position of the main channel. The city of Tucson is 
built upon the right bank of the stream, and Tumamoc Hill, the site of 
the Desert Laboratory, is on the opposite or left bank. 
The broad valley of Tucson has the appearance of being surrounded by 
mountain ranges on all sides. The view on the north and northeast is 

* Prepared by request and contributed by Prof. Wm. P. Blake, Sc.D., LL.D., 
Territorial Geologist of Arizona. 
