1920] Allen: Plankton of the San Joaquin River 7 



Location 

 SIMILAR GEOGRAPHIC LOCALITIES 



The San Joaquin River lies in about the same latitude as the larger 

 part of the Mediterranean Sea, the headwaters of the Tigris and 

 Euphrates, and a considerable portion of the Hoang Ho, both of head- 

 waters and lower reaches. It extends northwest from about 35° to 38° 

 N. latitude between 118° and 122° W. longitude. The main basin lies 

 on the isotherm of 60° P. Similar average tempei'ature conditions are 

 found in the Potomac region of the United States, along the northern 

 border of the Mediterranean Sea and in north central China near the 

 coast. Stockton lies in latitude 37° 57' 30" N., longitude 121° 17' 30" 

 "W. and on isotherm 60° (15.5° C). The altitude at the steamer 

 landing in mid-city is sixteen feet, according to Mr. A. L. Miner, assist- 

 ant city engineer. 



GEOGRAPHIC AREAS OF MIDDLE CALIFORNIA 



The part of California containing the San Joaquin sy.stem is a 

 region of great diversity, but it is quite distinctly composed of three 

 parallel strips of country. There is the Coast Range at or near the 

 western border of the state, the central plain known as the San Joaquin 

 Valley, and the Sierra on the eastern border. The part with which 

 we are immediately concerned is comprised in the eastern slopes of 

 the Coast Range, 4,000 square miles, the valley, 12,700 square miles, 

 and the western slopes of the Sierra, 16,000 square miles. The range 

 of altitude is from near sea level in the lower valley through some 

 hundreds and thousands of feet in the Coast Range and the Sierra 

 foothills up to over 14,000 feet in the High Sierra. The gradient is 

 slight lengthwise of the valley, very steep, commonly twenty to forty 

 feet to a mile, to the Coast Range, and generally moderate to the 

 Sierra, averaging nearly five feet to a mile. 



SIZE AND FORM OF SAN JOAQUIN DRAINAGE AREA 



The total length of the San Joaquin River is near 350 miles, 125 

 miles from the High Sierra to the main valley and 225 miles thence 

 to the outlet into Suisun bay, 50 miles from San Francisco. All the 

 important tributaries are from the Sierra slopes, which consist mainly 

 of granites and metamorphic rocks, sedimentary and igneous. The 

 slopes of the other side are mostly sandstone, shale and conglomerates. 



