SUBMARINE CHANNELS OFF THE PACIFIC COAST. 325 



to deep water. Professor Davidson, however, thinks that this may be due 

 to the scouring action of the powerful tidal currents characteristic of this 

 strait. Off the mouth of the Cohimbia river nothing remarkable has been 

 discovered ; and the mouths of the TJmpqua, the Rogue, and the Klamath 

 rivers have not been investigated. It may be, therefore, that the phenomena 

 on this part of the coast do not greatly differ from those on the eastern coast. 



But along the California coast the phenomena are quite different. The 

 researches of Professor Davidson have brought to light some twenty or more 

 submarine channels on the coast from Cape jMendocino to San Diego, a dis- 

 tance of about 700 miles. To mention only the most important: there are 

 four very marked ones within 25 miles of Cape Mendocino going southward, 

 and a fifth, long known and very distinct, in the Bay of Monterey. But 

 strange to say there is none off the Golden Gate. Going still southward, there 

 are two or more about the Santa Barbara sound, and one or two about San 

 Diego. These all have distinctive features of subaerial erosion-channels, 

 and show a former elevation of the continent of at least 2,000 to 2,500 feet 

 above its present level. But the distinctive feature about these, as contrasted 

 with those on the easteru coast, is that they have no obvious relation to exist- 

 ing rivers. They are not a submarine continuation of any system of river 

 valleys on the adjacent land. On the contrary, they run in close to shore, 

 and abut against a bold coast, with mountains rising in some cases to 3,000 

 feet within three to five miles of the shore-line, and wholly unbroken by any 

 large river valleys. It is impossible to account for this except by orogenic 

 changes which diverted the lower courses and places of emptying of the 

 rivers since the channels were made. Moreover, we can, I believe, fix with 

 more certainty than we can at the east the date of these changes. 



Orogenic History. — The Coast ranges of California, as is well known, were 

 formed at the end of the Miocene. Until that time, the Pacific shore-line 

 was somewhere east of the Coast range, and the place of this range was a 

 marginal sea bottom receiving abundant sediments in preparation for the 

 future mountain. Evidently, then, the hollowing out of the submarine 

 channels was the work of the Pliocene alone ; and the greatness of the work 

 was such that it must have occupied the whole Pliocene. It follows, there- 

 fore, that the orogenic changes which diverted the rivers from these chan- 

 nels must have occurred about the end of the Pliocene or beginning of the 

 Quaternary, and were therefore probably coincident with the enormous 

 orogenic changes, with lava-flows and consequent displacement of the rivers, 

 which took place at that time in the Sierra region. We have abundant 

 examples in the Coast range, also, of lava flows on a prodigious scale, even 

 forming mountain ridges. Such are the ridges 1,000, feet high, bounding 

 Napa valley on either side and culminating in Mount St. Helena, over 4,000 

 feet high. All the region about Clear lake and northward, is covered with 



