About 20 protesters have set up camp at an oil sands operation in eastern Utah.
U.S. Oil Sands was scheduled to begin mining this summer on school trust lands, where workers have dug a test pit.
Utah Tar Sands Resistance says such operations pose risks to wildlife and to water supplies used for drinking and irrigation.
State regulators and the company have insisted the eastern Utah desert is so dry there is little groundwater to pollute.
The company leases 50 square miles of Utah trust lands dotted with gooey bitumen, a tar-like form of petroleum.
Last summer, more than 50 protesters took credit for shutting down an operation there, but officials said nobody was working the tar sands pit and protesters managed only to chase away a road crew.