REPORT ON A COLLECTION OF PLANTS FROM THE 
PINACATE REGION OF SONORA. 
By J. N. Rose anp Paut C. STANDLEY. 
INTRODUCTION. 
An expedition was organized at the Desert Laboratory of the 
Carnegie Institution by Dr. D. T. MacDougal in the autumn of 1907 
for the purpose of making a general bio-geographical reconnaissance 
of the region between Tucson and the Gulf of California. Attention 
was to be directed chiefly to a comparison of the physical features 
of the coastal desert with those of the elevated arid area in which 
the Desert Laboratory is located and to obtaining data regarding 
the general features of distribution and environment of the higher 
plants and animals. 
The expedition left Tucson, Arizona, November 2, 1907, going 
westward 125 miles to the northern end of the Ajo Mountains, thence 
southward across the Mexican boundary to the village of Sonoyta, 
and westward through Santo Domingo and Quitovaquito. The 
course of the Sonoyta River was now followed southward to Agua 
Dulce where its waters are lost in the sands and then the route was 
laid across the desert to Monument 180 on the boundary, from which 
a departure was made that took the party southward along the 
western side of the Pinacate Mountains, the principal stations being 
Papago Tanks, Tule Tanks, and Pinacate Peak. In addition to this 
Mr. G. Sykes made a forced march to the shore of Adair Bay on the 
Gulf of California. 
The Pinacate Mountains are the highest in northwestern Sonora. 
They run north and south just east of parallel 113° 30’ longitude, 
between 31° 40’ and 31° 50’ north latitude. The highest peak, 
Pinacate, is about 1,218 meters in height, its slopes extending with 
but slight interruption to the shore of the Gulf. The entire range 
is of recent volcanic origin, with many sunken or elevated craters, 
the formations including great areas of volcanic sand, ashes, tufa, 
and hard lava, and the range lies in a vast field of broken lava which 
extends northward into Arizona. A careful survey of the region 
traversed was made by Mr. G. Sykes and his most excellent map is 
reproduced in connection with this article. 
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