Bundles containing 1,200 marijuana plants cut down by narcotics agents hours earlier were stolen - possibly by the illicit growers - from a site on the Mount Tamalpais watershed in the middle of the night, water district officials said Friday.

The stolen haul, part of 20,000 plants discovered at several West Marin pot gardens earlier in the week, was valued at roughly $3 million, according to estimates by narcotics agents.

"It was overnight on Tuesday when the plants were taken," said Paul Helliker, general manager of the Marin Municipal Water District. "Apparently some of the growers returned."

Disclosure of the theft came as details of the extensive marijuana operation - the largest ever detected in the county - were revealed by officials. Weapons, camps and sophisticated growing systems were found.

The bust sites and plants were being guarded by law enforcement overnight, but because individual gardens were scattered over remote locations, some areas were left unattended at times, officials said.

Authorities seized the 20,000 marijuana plants valued at an estimated $50 million in West Marin earlier this week.

Marijuana groves were found along a swath of the Bolinas Ridge from Kent Lake to Highway 1 to the Olema Valley. Some of the sites were in federal parkland, while others were on Marin Municipal Water District land.

So far, there have been no arrests. Fifty rangers and police narrowly missed the growers when they first raided the area Monday, finding hot, steaming scrambled eggs on dishes in a makeshift camp, one of several discovered.

"A couple of people escaped, and they knew the area well. They may have come back into the area undetected," Helliker said.

The stolen plants - some as tall as 12 feet - had been cut, bundled and were ready to be taken out from the remote location by helicopter, officials said.

Representatives of the National Park Service and Marin County Sheriff's Office, also in on the raid, were unaware Friday any plants had been stolen.

"The plants were being watched overnight, but they were grown over a very large, remote area," said John Dell'Osso, a spokesman for the National Park Service.

The nearest marijuana site was a 90-minute hike from the Bolinas Ridge Road on brushy, steep slopes.

The growing operation, believed to be one effort, was an extensive and highly-organized network of irrigation and marijuana plots, including six camps on water district land. A similar and larger operation was reported on the park service side of the ridge, according to a water district report on the operation.

Some camps had raised platforms where bedding and kitchens were off the ground, with other separate and higher structures that appeared to be lookout facilities.

Each camp served one or more marijuana gardens. The marijuana gardens were served by an extensive irrigation network. Several water collection systems supplied a set of deep, hand-dug, polyethylene-lined ponds that supplied gardens or other remote ponds lower on the slope, according to the water district.

The gardens contained about 1,000 plants each, fed by well-maintained drip irrigation systems. Terracing and individual, deeply dug planting holes were standard for each plot. Underbrush was cleared and trees were cut back to allow more sunlight in the gardens. Many trees were felled for use in camp structures. The camps also had facilities for drying and grooming plants.

There were thousands of feet of irrigation tubing covering the area, according to the report.

Camps typically included propane cook stoves, kitchen pots, pans and utensils, bedding, tarps, car batteries - possibly to charge cell phones - and fresh supplies of food. Vegetable gardens were common.

Other items found in the camps included fertilizer, peat moss, soil amendments, fish emulsion, granular rat poison, rat and mouse traps, thin-stringed deer barriers, insecticide, hand garden sprayers, small plastic seedling containers, empty backpacks, suitcases and hand tools.

Two pellet rifles and an empty box of .357 magnum bullets were found.

The camps appeared to be at least two years old, but could have been three to four years old, indicating growing had been occurring each summer for some time.

Officials will determine the age of the camps through tree ring analysis on the trees that were cut.