The Altar Valley Conservation Alliance is a collaborative conservation organization founded in 1995, and incorporated as a 501(c)3 not-for-profit organization. Just southwest of Tucson, Arizona, the Altar Valley comprises approximately 610,000 acres of Sonoran desert grassland, some of the most biologically rich and ecologically threatened biotic communities in the world. Private ranches work side by side with federal, state and local agencies to manage the valley, which is the largest unfragmented watershed in Pima County, outside of the Tohono O’odham Nation to the west. This collection is an archive of reports and other documents specific to Alliance activities.
Late Quaternary arroyo formation and climate change in the American Southwest
Geological Society of America
Abstract: Arroyos, entrenched ephemeral streams that form in desert environments, first appeared in the arid and semiarid American Southwest after 8000 14C yr B.P. For at least 7 k.y. prior to that time, climate, vegetation, and groundwater conditions were not conducive for arroyo formation along the floors of desert valleys. After a hiatus in arroyo formation, the frequency of arroyo cutting and filling increased dramatically after 4000 14C yr B.P. The early Holocene arroyos and increased frequency of arroyo incision after 4000 14C yr B.P. are related to the establishment and changes in postglacial vegetation, climate, and groundwater conditions. As a result, arroyo sequences preserve a record of large-scale climate change and small-scale climatic perturbations that occurred during the Holocene. Human modification of valley flood plains is an additional factor that contributed to mid-nineteenth and early twentieth century arroyo cutting.
Name of Journal:
399 - 402