94 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



species. They collected on the north end of the island, chiefly at Puerto 

 Refugio. Dawson has 4 numbers from Pond Island, a small rocky body 

 connected with the east side of the Angel de la Guardia at low tide. 

 Their collections add 6 species to the known flora of Angel de la Guardia 

 Island, one of which is new to science, Lyrocarpa linearifolia. 



Tiburon Island is the largest in the gulf. It is separated from the 

 Sonoran mainland by a shallow narrow channel, *'el infiernillo," two 

 to five kilometers wide and only three to four meters deep. Roughly 

 quadrangular in shape, the island contains about 1170 square kilometers. 

 Although mountainous, there are extensive valleys and several "aguajes," 

 where fresh water is available for indeterminate periods following rains. 

 On the north end, where Bahia Agua Dulce roundly indents the shore 

 line, there is a permanent fresh water spring. In former times it was 

 regularly used as a base settlement for the seminomadic Seri Indians, 

 who still occasionally roam over the island hunting, fishing, and forag- 

 ing upon the native wild plants and animals. There are two igneous 

 ranges of mountains trending north and south and paralleling the ad- 

 jacent ranges of Sonora. The western is Sierra Menor, the eastern and 

 higher is Sierra Kunkaak (the Seri name for it) with a middle peak 

 elevation of 1218 meters. 



A porphyritic granite occupies the southeast part of the island, ac- 

 cording to Jones (1910), who explored the island. He traversed the 

 island north to south along the east side, east to west across the south 

 end, and went into the interior around the highest peak. The greater 

 area of parent rock is volcanic. ''The types are profuse and belong to 

 the effusive class." Also present are andesite, rhyolite, *'the latter pass- 

 ing into the extreme phases of obsidian and pumice." No limestone or 

 other sedimentaries were observed by him and his party. The volcanics 

 may be a part of the Upper Miocene pyroclastics (Comondu formation), 

 which predominate much of the California gulf area, although Jones 

 took them to be much younger. 



The vegetation and the flora, so far as known, appear closely re- 

 lated to that of the adjacent mainland (Plate 9, fig. 21). This is to be 

 expected, since the shallow infiernillo channel was emerged repeatedly 

 during the low sea levels of the glacial periods. The land bridge would 

 then have allowed plant migration to or from the island, excepting those 

 plants restricted to the rocky slopes and which find the sandy lowlands 

 intolerable. The dry rocky slopes support a dispersed Desert Shrub for- 

 mation, while the bottomlands and aggrading surfaces are thinly forested 



