10 University of California Publications in Zoology [Vol. 22 



very rough, with bare, glaciated rocks of granite in the upper parts. 

 Altitudes vary from 300 feet in the foothills to 12,000 or 13,000 feet 

 at the divide. Upper parts have no forests, hut there is a median 

 belt heavily forested with coniferous trees. The lower region has only 

 grass and brush, usually. There is about 1,200 square miles of National 

 Forest in the mountains. Precipitation is about ten inches per annum 

 in the region near the junction with the San Joaquin, 25 or 30 miles 

 from Stockton. It ranges to sixty inches at high altitudes where most 

 is snow, the greater part of which disappears in spring. 



The Stanislaus River 



The Stanislaus River has a long, narrow basin, about 75 miles in 

 length and an area of somewhat over 950 square miles. The length of 

 the river is about 120 miles, 80 miles in the mountains. The source is 

 mainly in glacial lakes about the divide and the mouth is about 20 

 miles above Stockton. The general character of the basin is quite 

 similar to that of the Tuolumne. 



The Calaveras River 



The Calaveras River flows near Stockton and empties six or seven 

 miles below the city. It has some influence in flood season on account 

 of the overflow, but in this case its influence would be much the same 

 as that of those already mentioned since the flood waters of all are 

 essentially similar. Furthermore, the flood waters of the Calaveras 

 are largely kept from the San Joaquin above Stockton by an enor- 

 mous levee forming the so-called "diverting canal." 



TURBIDITY 



The turbidity of the water of the San Joaquin in the vicinity of 

 Stockton at all times of the year is very characteristic. In the river 

 channel this is obviously due to fine silt during the flood season but 

 the plankton is the principal source in the sluggish water of late fall. 

 Water in some of the sloughs sometimes becomes clear enough to 

 reveal objects at a depth of six or eight feet. 



