Three federal biologists were held at gunpoint for several minutes by suspected members of a Mexican drug cartel after happening upon a large marijuana patch in a remote stretch of public land in northern Nevada, authorities said Friday.

The men, conducting research for the Bureau of Land Management, were released unharmed after being held by three men Tuesday afternoon in the high desert about 200 miles northeast of Reno, near Winnemucca, said JoLynn Worley, an agency spokeswoman.

Law enforcers returned to the scene Wednesday and found that the suspects had fled, leaving behind a makeshift camp indicating that as many as six people were involved. Authorities confiscated nearly 800 mature marijuana plants with an estimated wholesale value of $5 million, as well as about 150 pounds of processed buds, BLM officials said.

"This is the first time in Nevada that BLM employees have actually come upon people (at a marijuana garden) and been threatened," Worley said. "I'm not aware of it in any other Western state, either."

The unarmed biologists were conducting a stream survey when they encountered three men and the pot garden, which stretched for nearly a mile along the North Fork Little Humboldt River, authorities said. Law enforcers said that two men carried handguns and that the third had a rifle with a scope on it. The men were Hispanic; investigators did not say why they suspected the men were part of a Mexican cartel.

After a tense 10-minute standoff, the BLM employees were told they could leave but ordered to go in the opposite direction because the armed men said there were other people in the direction the BLM workers were headed, Worley said.

The employees retreated and hid until darkness fell. They were picked up late Tuesday by a BLM search party as they walked along a gravel road toward the community of Paradise Valley, she said.

"I know they were shaken, and it was certainly a very frightening encounter," Worley said.

The BLM, the Humboldt County Sheriff's Office and the Nevada Department of Public Safety Investigative Division are investigating.

The BLM, which manages most of Nevada's land, warned the public to be aware of their surroundings in remote areas.

"Basically, any area that is out of the way and has water could be potentially a place for people to grow a pot garden," Worley said.