Pro tip: We found a whole new layer of a site in Tucson after a flash flood washed away a foot of topsoil.

I was on a crew digging at a known Hohokam site near the Santa Cruz River last spring. The storm cleared out a bunch of modern fill and exposed a previously buried pithouse floor. Now we always schedule a walkover survey after heavy rain. What's the biggest 'accidental' find you've seen change a dig plan?