Geol— Vol. I.] DAVIDSON— SUBMERGED VALLEYS. 97 



21. The Cape Mendocino Submerged Valley. 



This is the fourth and northernmost of the Mendocino 

 series. The distance between Point Gorda and Cape Men- 

 docino is 12 miles, with a very slight recession of the in- 

 tervening shore-line to the eastward. The mountains come 

 to within three miles of the ocean, with a height of 2,600 

 feet; at ten miles inshore they reach 3,400 feet. 



We have shown that the Mattole or Punta Gorda sub- 

 merged valley lies just north of that point ; and yet within 

 four miles of it to the northward enters the northenmost of 

 this group of remarkable submerged canons. This fourth 

 valley lies under the southern edge of the relatively broad 

 plateau that makes out six miles to the westward of Cape 

 Mendocino, with only 55 fathoms. More detailed sound- 

 ings have not been made. On the line of this 55 fathoms 

 the valley has a depth of 500 fathoms and heads in nearly 

 east to 25 fathoms about i^ miles from the shore. It has 

 steep sides; and in one place, on the north side, the drop 

 is 250 fathoms or 1,500 feet in half a mile. As in the other 

 three valleys, the bottom on the adjacent plateau has many 

 points of green or black mud as far in as 25 fathoms. The 

 valley itself has green mud, and yet in two places at depths 

 of 320 fathoms broken shells were brought up with gravel. 

 Both slopes of the valley have green mud up to 30 or 35 

 fathoms, when the bottom changes to fine gray sand. 



The geographical position of the head of this valley in 

 25 fathoms is: 



Latitude 40° 23' north; longitude 124° 24' west. 



Northward of this valley the irregular and comparatively 

 shoal bottom off Cape Mendocino, marked by Blunt's Reef 

 and other dangers, stretches out well to the westward of the 

 usual coast depths, and is thence spread out towards Hum- 

 boldt Bay and Trinidad Head as a broad plateau inside the 

 lOO-fathom line. 



The occurrence of these four characteristic submerged 

 valleys within a lineal coast-line of 22 miles is remarkable. 

 Cape Mendocino and the adjacent high coast is the 



