DeChristopher is charged with interfering with and making false representations at a government auction. He faces up to 10 years in prison and $750,000 in fines if he's convicted.
Prosecutors have offered DeChristopher plea deals over the past two years, but he opted to go to trial. He plans to testify.
The case has become a symbol of solidarity for environmentalists who want to protect the parcels of land, which totaled 22,500 acres around the two national parks.
About 400 people, including actress Daryl Hannah, gathered for a rally Monday, singing Pete Seeger's protest song "If I Had Hammer," criticizing government control of public lands and waving signs that called for DeChristopher to be "set free."
Hannah said she believes DeChristopher's actions have been justified because the federal judge turned back the leases.
"He took a moral stand against injustice. ... He's already been effective," Hannah said. "This case has the potential to be quite historic and pivotal in terms of our rights as citizens to peacefully protest and practice civil disobedience."
Federal prosecutors say DeChristopher is the only person ever charged with failing to make good on bids at a lease auction of public lands in Utah.
Not everyone attending the protest march Monday supported DeChristopher's actions.
Real estate agent Robert Valentine mingled with environmentalists and talked about the need for Utah to use its natural resources to create jobs and fund the state's schools.
"I want to protect the natural resources. My hobby is hiking," the 69-year-old Valentine said. "But I think Utah ought to be allowed to have more control over the resources more than we do."
The trial was expected to last until Friday.
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