LA CIÉNEGA DE SANTA CLARA, MÉXICO— Alejandra Calvo crosses a barren stretch of desert in Sonora, México almost daily during certain times of the year. The route could easily disappear beneath blowing dust and when rain does fall here, it renders the road impassable. There are no birds or wildlife here, not even any visible plants. It wasn’t always like this: Until the 1960s, the Colorado River spread across this delta on its path to the Sea of Cortez. Originally from Chiapas, Calvo is a biologist who works for ProNatura Noroeste, a conservation group based in northwestern Mexico.