92 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



Sierra GIganta, which blocks the westerlies that cool the opposite side 

 of the peninsula. The vegetation is dominated by a dispersed, succulent, 

 microphyllous Desert Shrub with scattered small trees which increase 

 in stature and in number of species up in the steep canyon. Among 

 these latter are Bursera sp., Lemaireocereus Thurberiy Cercidium molle, 

 and the palm Erythea Brandegeei, 



Four collections have been made from Puerto Escondido and vicinity, 

 mainly in the canyons cutting steeply back into the mountains of Sierra 

 Giganta. 



I. M. Johnston May, June 1921 50 num.bers 



P. J, Rempel March 1937 30 numbers 



H. S. Gentry April 1938 50 numbers 



E. Y. Dawson February 1940 25 numbers 



It should be noted that all collections were made in the spring and 

 that the late summer flora fostered by the summer rains has not been 

 collected. Due to the precipitous slopes, the arid climate, and the tor- 

 rential type of rains, the soils are rankly immature. The humic soils 

 are confined to pockets in rocks, or to riparian embayments, and in 

 them are commonly found the small succulents (e.g. Mammillaria) 

 and mesophytes of erratic dispersion. In the high, narrow, and rocky 

 canyons, where shade and run-ofiF conserve and augment soil moisture, 

 there are found many subtropical species of the wetter Cape District. 

 Pachycormus discolor here forms one of the largest trees with erect 

 straight trunks 30 feet high or more, presenting quite a different habit 

 from the dwarf contorted members of the species found in more arid 

 habitats on the peninsula. Quercus idonea occurs in the mesic saddles 

 and slopes near the tops of the Sierra Giganta. 



In the sierran area about Puerto Escondido, including the collect- 

 ing localities of Agua Verde Bay 25 miles to the south and Comondu 

 on the other side of the mountains, there are several plants having local 

 distributions. These include Verbesina oligocephala, Polygala apopetala, 

 Ruellia cordata, Cercidium molle, Dalea vetula, Mimulus sp., Perityle 

 aurea, Agave sohria, and Vallesia laciniata. Their limited distributions 

 corroborate the little geologic evidence gathered to date that indicates 

 insular periods during the Tertiary for the Sierra Giganta area. 



Angel de la Guardia Island, lying close along the peninsula, is 

 the second largest of the gulf islands. It has an approximate area of 

 975 square kilometers and the highest peak is 1315 meters above sea 

 level. As indicated in Plate 8, figs. 18-20, the island is rugged, "barren," 

 with precipitous slopes, and canyons shortly discharging into the sea. 



