Collectors can gather up to 250 pounds a year with a permit, but the wood cannot be taken for commercial purposes.
Heavy equipment and explosives are illegal, too.
''When you see the massive, beautiful petrified logs that have been taken, you'll be sick,'' said rancher Wally Stout, 64, who reported the thefts in Washington County.
''People have been taking little pieces of petrified wood from this area for a long, long time. But the current flurry of activity is of a large scale,'' he said.
Long, empty trenches now occupy the space where 60-foot-tall logs stood on U.S. Bureau of Land Management land near Virgin, he said.
The BLM has the authority to take criminal or civil action against violators.
Petrified wood can be found at rock shops for less than $100 for small pieces to several thousand dollars for museum-quality pieces.
