2 g<5 NATURAL HISTORY BULLETIN. 



Tucson and reaches the Colorado river — at the latter place 

 the screw-bean {Prosoftis} abounds. 



Work was begun at Tucson, which lies at an altitude of 

 about 2,400 feet, 1 in the valley of the Santa Cruz river, an 

 insignificant stream except when swollen by the heavy rains of 

 July and August. In the immediate vicinity of town the 

 ground is mostly flat, though rugged and rocky hills are with- 

 in easy walking distance, while farther away rise the moun- 

 tains which nearly surround the plain. To the eastward looms 

 the Santa Catrina range; the Santa Rita Mountains are about 

 thirty miles to the southward, while the Tucson Mountains lie 

 more to the west, The vegetation of the Santa Cruz Valley, 

 except in the river bottom, consists of such plants as can flour- 

 ish in a gravelly or sand}' soil of such porous nature that it 

 dries almost at once after a rain. In consequence we find 

 mesquite, screw-bean, various other thorny leguminous shrubs, 

 the "-palo verde" and the like. Cerens giganteus, the giant 

 cactus, the fruit of which is sought after by the Indians, and 

 various other cacti, flourish here. Opnntias grow to a con- 

 siderable size and fruit in profusion. "Montezuma's compass" 

 a great cactus of nearly the size and shape of a nail-keg is 

 often met with. There is no turf, such grass as exists being 

 scattered. 



The first stop at Tucson was made simply as a necessary 

 preliminary to a trip across the country in the direction of the 

 upper Gila River. Consequently on the morning of June 16th 

 I took the train for Casa Grande which is a small settlement 

 in a semi-desert region and owes its chief interest to the ruins 

 of the great Aztec house near by. The altitude is said to be 

 1398 feet. But little collecting could be done as the stage left 

 in a few hours for Florence and Riverside, the latter being 

 my immediate destination. The ride was very enjoyable, 

 since beyond Florence the road passed directly through the 

 giant cactus belt and the effect of these great trunks in the 

 semi-darkness of evening was extremely weird. 



1 The altitudes quoted are taken from Bull. No. 5, of the U. S. Geolog- 

 ical Survey, Washington, 18S4. 



