The Geologic Origin of the Sonoran Desert Geology challenges the
human imagination. First of all, there is the notion of geologic
time. We humans think in terms of lifetimes or of centuries.
What can 10,000 years possibly mean to us, let alone 65,000 or
70 million? Space, in geologic terms, is an equally difficult
notion, though we don't often recognize the difficulty. We often
wonder what the land we stand on was like in times past. What
was here, we ask, when dinosaurs roamed, or when mountains were
new? Though we may imagine different landforms, different
vegetation, we probably still imagine "here" as a definite, and
permanent, spot on the globe, a place with constant longitude
and latitude, a place whose changes we could trace through time,
perhaps by reading the record in the strata beneath our feet.
But geology mocks our notion of permanence. Geology deals with
continents that drift, collide and re-form, with rivers and
oceans that appear and disappear, with mountain ranges whose
battered remnants have