Police arrested a Pittsburg man Wednesday morning after finding 1,800 marijuana plants growing in an isolated part of the Las Trampas Regional Wilderness near San Ramon, East Bay Regional Parks police said.

Authorities say Policarpio Gallegos, 63, of Pittsburg, lived at an encampent on the site, which is in unincorporated San Ramon about a half-hour away from the nearest hiking trail.

Police spotted a second man at the camp, but he got away.

Investigators from the Contra Costa County Sheriff's Office, the state Department of Justice and the Alameda County Sheriff's Office raided the camp this morning. Both men ran from police, but only the one got away, according to the parks district.

The suspect who escaped was described as Latino, in his 30s, about 150 pounds and about 5 feet 8 inches tall, said Shelly Lewis, spokeswoman for the parks district. He had brown hair and brown eyes and was wearing faded denim pants and a light brown shirt, she added.

Lewis said the street value of the pot was about $225,000, according to a Department of Justice estimate. Authorities believe the camp was part of a larger operation.

"We're sure it wasn't just these two men," Lewis said.

The suspects had set up a tent and a couple of sleeping bags on the site. They were pumping water out of a nearby creek to water the crops and used a generator for electricity. There were no guns or weapons found on site, and no one was hurt during the raid.

"This wasn't the most elaborate or the largest setup we've seen," said Lewis. "But it was bigger than many."

She said the regional parks district finds at least one marijuana grow a year, some of them much more elaborate than the one busted this week.

A parks helicopter first spotted the encampent a couple of weeks ago but wanted to wait for the heat wave to end before dismantling it.