Note IV'-37 — Chapter IV · OBSERVATIONS ON NEW SPAIN.[IV'-1]

The whole Sonoran water-shed is Pacific, and the river-system runs on general S. and S. W. courses to the Gulf, in a series of somewhat parallel streams. The northernmost one of these, of any size, which Pike calls Ascencion r., I find lettered Rio Altar; its main branch is Rio Magdalena; some of its ultimate sources are in Arizona, in the country about Arivaca, Tubac, and old Fort Mason; it discharges between George's bay and Cape Tepoca. The Sonora is much larger, with a main branch called San Miguel; it discharges opposite Tiburon isl. Arizpa, which Pike speaks of as near the head of the Yaqui, is high up on the right bank of the Sonora; lower down is Hermosillo (lat. 29° 10´ N., long. 110° 45´ W.). The Yaqui is the largest Sonoran river, falling into the Gulf below Guaymas and above Point Lobos. It has two main forks, Rio Moctezuma and Rio Bavispe. Rio Matape, a small river, is the one that falls in at Guaymas, and not the Yaqui. Another small one, Rio Mayo, falls in below Vacamora and Point Rosa. Rio Alamos, which heads in Sonora, falls over the Sinaloan boundary.