BISHOP, Calif. (AP) - Carvings that graced the Sierra Nevada in California for thousands of years have fallen prey to modern thieves armed with power saws.

The Los Angeles Times says at least four petroglyphs - some of them located 15 feet above the ground - have been hacked off of lava cliffs in the Eastern Sierra.

The region, known as Volcanic Tableland, is held sacred by local Indian tribes whose ancestors carved hunting images and spiritual designs into lava boulders.

Visitors reported the thefts on Oct. 31. A Bureau of Land Management archaeologist calls it the worst act of vandalism he's ever seen in the area.

Volunteers have stepped up surveillance in the area and authorities are offering a $1,000 reward for information leading to arrests.

Copyright 2013 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.