Holocene Vegetation of the Hornaday Mountains of Northwest Sonora, Mexico

Van Devender, Thomas; Burgess, T.; Felger, R.; Turner, R.

The 94 taxa of plants identified from 10 packrat middens from 240 to 260 m elevation in the granitic Hornaday Mountains provide an excellent history of vegetation and climate for the last 10,000 yr B.P. in the Pinacate Region of northwestern Sonora, Mexico. Rocky slopes in this arid area (ca. 120 mm/yr precipitation) in the Lower Colorado River subdivision of the Sonoran Desert have supported desertscrub communities dominated by Encelia farinosa (brittlebush), Larrea divaricata (creosotebush), and Carnegiea gigantea (saguaro) throughout the Holocene. Community composition charged continuously on both long (10,000 yrs) and shorter time scales. Ephedra nevadensis (Morman tea), condominant with Encelia farinosa, Larrea divaricata, and Carnegiea gigantea in early Holocene (8910 to 10,000 yr B.P.) samples, and rare Juniperus cf. californica (California juniper) imply a continuation of the cool summers and primarily winter rainfall of the late Wisconsin glacial. Middle Holocene (4430 to 8660 yr B.P.) samples contained trees and shrubs such as Acacia greggi (catclaw acacia)