SUBMARINE VALLEYS ON THE PACIFIC COAST. 265 



SUBMARINE VALLEYS ON THE PACIFIC COAST OF THE 

 UNITED STATES. 



BY GEORGE DAYIDSON, 



Read at tbe Meeting of October 4tli, 1886. 

 (This paper was illustrated with diagrams.) 



The plateau of the Pacific Ocean reaches a depth of 2,000 

 to 2,400 fathoms within as little as forty or fifty miles of the 

 Coast to the southward of Cape Mendocino. The descent 

 to these profound depths is not uniform, however, except 

 off the high range of the Santa Lucia. Generally there is a 

 marginal plateau of ten miles out to the hundred fathom 

 curve, and then the descent is sharp to five or six hundred 

 fathoms. Off the level and shallow plateau of the Gulf of 

 the Farallones, the descent is rapid within five miles of the 

 South East Farallones, and reaches 2,000 fathoms in fifty 

 miles. The determination of these great depths we owe to 

 the deep sea soundings of Commodore Belknap, of w^hich 

 a full discussion was presented by me to the Academy in 

 1873-4. 



Into this marginal plateau of one hundred fathoms there 

 have been developed, in the course of the operations of the 

 United States Coast and Geodetic Survey, several remarka- 

 ble submarine valleys. Notably that in Monterey Bay, 

 heading to the low lands at the great bend of the Salinas 

 River; and that off Point Hueneme at the eastern entrance to 

 the Santa Barbara Channel, also heading into the low coast 

 at the wide opening of the Santa Clara Valley . Then there 

 are one or two near the mouth of the Laguna Mugu, two or 

 three ofi' the southern point of Carmel Bay, while the deep- 

 est one enters far into the Bay. These all have remarkable 

 characteristics which I have heretofore brought to the no- 

 tice of the Academy. 



