96 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



early springs 1937 and 1940, when their collections were made, appar- 

 ently were too dry for general floral response. The summer-fall flora 

 of San Esteban Island is not known, all collections having been made in 

 the spring, Table 6. The known flora consists of 48 species. The Rempel 

 and Dawson collections are annotated in the following catalogue of 

 species. 



San Pedro Nolasco is a rocky island 8 to 10 miles off the Sonoran 

 coast along the latitude of Guaymas (N 28°). About 3.5 kilometers 

 long and 1 kilometer wide, it is approximately 3.5 square kilometers in 

 area, and reaches a height of 315 meters. Like most of the gulf islands, 

 it rises sharply w^th steep rocky slopes out of the restless sea. Landings 

 have been made on the southeast side, where a narrow rocky defile leads 

 up into the interior. No source of fresh water has been reported. It is 

 reported as both volcanic and granitic (Fraser 1943:137, 149). Judging 

 from its stage of weathering (Plate 9, fig. 22), it is a youthful island, 

 but its age is unknown. 



In accordance with the rocky slopes there is a heavy succulent ele- 

 ment in the vegetation represented by Pachycereus Pringlei, Lemaireo- 

 cereus Thurberi, Fouquieria peninsularis, Agave chrysoglossa, Pedilan- 

 thus macrocarpus^ and several smaller inconspicuous cacti (Plates 10, 11, 

 figs. 23-26). In addition to the tree cactus listed above there are Bursera 

 micro phylla, the peninsular Ficus Pahneri, and the Sonoran Acacia Wil- 

 lardiana. Unique also is the extensive growth of a bunch grass, Setaria 

 macrostachya, which Johnston reports (1924:987), "extremely abun- 

 dant on north-facing slopes on San Pedro Nolasco Island (4397) where 

 it makes some hillsides appear like hay fields." This odd assortment of 

 flora is dominantly composed of rock-inhabiting species and suggests for- 

 tuitous occupancy characteristic of an infant island. The island appears 

 too young for soils and maturely balanced plant communities to have 

 developed. Comparable pioneer societies have been noted on the recent 

 volcanics of the adjacent mainland, as on the southwestern out-lyers of 

 the Bacatete range along the Sonoran coast. 



The known flora (Table 7) consists of 27 species, of which 8 have 

 been added by the Velero III collections, represented by 15 numbers 

 collected by Rempel and Dawson as annotated below. The iguana 

 {Ctenosaura hemilopha) is a conspicuous resident. 



The Guaymas monadnock consists of a discontinuous range of cer- 

 ros with intervening and bordering valleys and plains. The area has a 

 certain physiographic unity and comprises about 3000 square kilometers 

 with a peak elevation of 1316 meters. Clifl and rocky slopes form an 



