How to find rocks worth tumbling? My son recently got a rock tumbler and I was wondering if anybody knows of any resources that would show pictures of the different types of rocks as they would be found on the ground. I live in Chino Hills CA and we have many trails. I wanted to be able to tell the difference between something worth tumbling and something that isn't.
Any stone quartz rich and smooth not porous (no visible holes) like agates, quartzite or cherts are you best bet for getting a nice tumbled stone.

A great book is:

Gems and Minerals of America: A Guide to Rock Collecting (1st Edition)
by Jay Ellis Ransom
Hardcover, 705 Pages, Published 1975

ISBN-10: 0-06-013512-3        / 0060135123
ISBN-13: 978-0-06-013512-6 / 9780060135126

Your local library might have a copy of it.
See to find on sale on Internet also: used ~$5.00

http://www.gettextbooks.com/isbn/9780060135126

BTW, tumbling stones and rock collecting led me to a career as a geologist.