San Juan County Sheriff Rick Eldredge said from 40 to 50 people, many of them waving American flags, drove about a mile down Recapture Canyon near Blanding and then turned around. Hundreds attended a rally at a nearby park before the protest.
"It was peaceful, and there were no problems whatsoever," the sheriff told The Associated Press.
About 30 deputies and a handful of U.S. Bureau of Land Management law enforcement personnel watched as protesters drove past a closure sign and down the canyon located about 300 miles southeast of Salt Lake City.
Recapture Canyon is home to dwellings, artifacts and burials left behind by Ancestral Puebloans as many as 2,000 years ago before they mysteriously vanished.
Bureau of Land Management Utah State Director Juan Palma, in a statement, said the riders may have damaged artifacts and dwellings that "tell the story of the first farmers in the Four Corners region" of Utah, Arizona, New Mexico and Colorado.
"The BLM was in Recapture Canyon today collecting evidence and will continue to investigate," Palma said. "The BLM will pursue all available redress through the legal system to hold the lawbreakers accountable."
Bureau of Land Management officers recorded and documented protesters who traveled into the closure area, he added.
The agency warned riders all week to stay out, vowing prosecution against those who ignore a law put in place in 2007 after an illegal trail was found that cuts through the ancestral ruins. The canyon is open to hikers and horseback riders.
Utah Gov. Gary Herbert also urged people to uphold the law.
The group's act of defiance marks the latest illustration of growing tension between angry rural Western residents and the federal government over management of public lands.
San Juan County Commissioner Phil Lyman, the protest's organizer, has said it was designed to show that the federal agency isn't the "supreme authority" and local residents have a right to have their opinions heard. He did not immediately return a telephone call after the protest.
The protest occurred nearly a month after southern Nevada rancher Cliven Bundy and his supporters, some of them armed militia members, thwarted a Bureau of Land Management roundup of his cattle near Bunkerville, Nevada, 75 miles northeast of Las Vegas. Bundy, a states' rights advocate who refuses to acknowledge the authority of the federal government, owes more than $1 million in fees and penalties for letting his cattle use government land over the past 20 years.
Some of Bundy's children and militia supporters also took part in the protest in Recapture Canyon.
"This is where it's happening Saturday," Bundy backer Ryan Payne of Montana told the Las Vegas Sun. "This is a continuation of the Bundy affair."
A 14-mile section of trail in the canyon is closed to motorized vehicles, Bureau of Land Management officials said, but there are more than 2,800 miles of trails open to them on public lands around Blanding.
Environmentalists and Native Americans criticized the protest ride, saying the ban is needed to preserve fragile artifacts. Mark Maryboy, a former Navajo Nation Council delegate, called it disappointing that the group had no respect for Native American culture.
"The American tradition of civil disobedience doesn't change the fact that the rule of law needs to mean something," Josh Ewing of the conservation group Friends of Cedar Mesa told The Salt Lake Tribune. "I'll be very disappointed in my government if it doesn't follow through on upholding the law."
Motorized access to Recapture Canyon and other areas in Utah's wilderness has been a source of tension for decades. ATV riders rode another off-limits trail in 2009 in a protest. The Bureau of Land Management gave information about the riders to federal prosecutors, but no charges were filed.