Via PhysOrg:

In the summer of 2002, a week of heavy rains in Central Texas
caused Canyon Lake — the reservoir of the Canyon Dam — to flood over
its spillway and down the Guadalupe River Valley in a planned diversion
to save the dam from catastrophic failure. The flood, which continued
for six weeks, stripped the valley of mesquite, oak trees, and soil;
destroyed a bridge; and plucked meter-wide boulders from the ground.
And, in a remarkable demonstration of the power of raging waters, the
flood excavated a 2.2-kilometer-long, 7-meter-deep canyon in the
bedrock.