What hides this stereogram?

Driving down a remote road, a motorist sees a sign that says: "Watch For Fallen Rocks."

A couple of miles of careful driving later, he spots some pebbles and stops to pick a few up. Arriving in the next town, the motorist carries the stones into the highway maintenance office.

Placing them on the counter, he says to an official: "Here are your fallen rocks. Now where's my watch?"