The sandstone In Rock City is made from weathered bits of Sierra Nevada granite. Ken Lavin explains how those mountains moved—and helps us recognize the constituent parts, including quartz, feldspar, biotite and hornblende.

This tour of Mount Diablo's ROCK CITY is presented by Mount Diablo Interpretive Association. Featuring Ken Lavin, Rich McDrew, and Mike Woodring; Music: Phil Heywood; Production, Narration: Joan Hamilton; Photos: Seth Adams, Contra Costa Historical Society, Joan Hamilton, Moose Henderson, Ken Lavin, Conrad Lowry, Mark Sinclair; Special thanks to Anastasia Hobbet, Conrad Lowry, Jennifer Roe, Jerry Schweickert, Mark Sinclair, Stephen Smith.