In early spring, George Okoko was perched on a ledge 15 feet up a crumbly cliff, trying to whack off a basketball-size piece of rock with a hammer and chisel ... kinds of rocks, roads, buildings ...

Weathering and erosion slowly chisel, polish ... Weathering is the mechanical and chemical hammer that breaks down and sculpts the rocks. Erosion transports the fragments away.

and figures carved into the stone with a hammer and chisel. Petroglyphs provide a fascinating glimpse into the past no matter ...