NO. 2 gentry: land plants 43 



CEDROS AND SAN BENITO ISLANDS 

 Cedros Island is a partially submerged mountain that stands about 

 midway along the coast of Baja California across the broad Vizcaino 

 Bay. North to south it is about 38 kilometers long, averages about 8 

 kilometers wide, and contains about 300 square kilometers of rugged 

 land. It has several peaks, the highest of which is about 1200 meters 

 above the level of the Pacific Ocean. Dissected by numerous canyons, 

 some of which dip steeply to the sea, it contains several physiographic 

 habitats; peak, ridge, hill slope, mesa, canyon, cliff, and brief narrow 

 beaches. Alluvial slopes and valleys are notably minor. Salty and other- 

 wise highly mineralized and unpalatable water is reported to stand in 

 the lower reaches of the canyons. Near the south end of the island, 

 about 3 miles from what was formerly known as Bernstein's abalone 

 camp and at about 600 to 900 meters elevation, is a good fresh water 

 spring. Fishing has recently been developed by the construction of a 

 large cannery in the locality and a village has grown up around it. 



The island is composed mostly of sedimentary rocks. The south end 

 shows fossiliferous marine sediments of Cretaceous shales, Miocene 

 shales and sandstones, and Pliocene sands and conglomerate. Near the 

 middle of the east side of the island, "Grand Canyon" cuts back deeply. 

 G. Dallas Hanna, paleontologist on the California Academy of Science's 

 expedition to the Eastern Pacific islands in 1922 and 1923, wrote in 

 reference to the middle section, as follows (1926:88): "It was found 

 that a fault line crosses the island following approximately the course 

 of the canyon. To the south only, Jurassic cherts, supposedly Franciscan 

 in age, were found. To the north there is a block of Cretaceous shales, 

 200 or more feet thick, with a generally westward dip of about 30°. 

 — Our studies convinced us that Cedros Island is a zone of intense 

 block faulting and disturbance. At the present time, except for a com- 

 paratively recent post-Pleistocene uplift of little significance, the island 

 is in a period of depression. In other words, at no very distant period 

 geologically, the island was a part of a much higher land mass." He 

 found igneous rocks only at the two extremities of the island. "At the 

 southwestern corner of the island there has been some volcanism and at 

 the north end the land is greatly disturbed with intrusions of serpentine" 

 (1925:268). 



Since the axis of Cedros Island is aligned with that of Sierra Viz- 

 caino to the south on the western edge of the peninsula, and because 

 soundings show the intervening channel to be only 9 to 12 meters in 



