It would take 7,000 pickup trucks to haul off the muck, mud and rock that flooding left at the nation's most secure military outpost.

Boulders weighing tons still blocked lanes Wednesday near the entrance to the underground Cheyenne Mountain Operations Center, and experts said it would take weeks to clean up the damage left by a storm that hit on Sept. 12, dropping 14 inches of rain in hours.

"It overwhelmed the system," said Col. Travis Harsha, installation commander at the mountain.

The base sits high on the eastern slope of Cheyenne Mountain, carved into near-vertical granite. When rain strikes, Cheyenne Mountain is usually well-equipped to deal with the runoff through drainage channels and retention ponds.

But it was never designed for the deluge that hit Sept. 12.

"You don't want to design for a load like that," said Dino Banaldo, the mountain's top civil engineer and director of its emergency operations center. "It's not cost- effective."

The mountain base was constructed in 1961 at the height of the Cold War. It was designed to withstand a nuclear blast.

For decades it served as the nerve center for the North American Aerospace Defense Command, which is tasked with warning of attacks on North America.

In recent years, the mountain's mission has changed. NORAD uses less than a third of the underground complex as new, highly secretive tenants have moved in. The work underground is mostly classified.

During the rainstorm, those tenants had some leaks.

Caves everywhere tend to drip water and the mountain is no exception. The rock walls are lined, and workers do their jobs inside "buildings" constructed in the tunnels.

In the aftermath of the storm, more than 500,000 gallons of excess water - enough to fill a competition swimming pool - was pumped from the tunnels.

Apart from the water, which caused cosmetic damage to a few underground rooms, the underground facility survived the storm unscathed.

"It's designed to survive a nuke," Banaldo said.

But outside was a different story.

Harsha said the flow down the mountain left 12 feet of debris blocking the north entrance, including two boulders as large as buses.

Runoff began to undermine NORAD Road, a steep grade which leads to the installation.

"We would have lost that road if we hadn't acted as fast as we did," Harsha said.

The mudslide was spotted by guards and security cameras as soon as it hit. Harsha and other leaders were notified and rushed to the mountain.

The first job: calling the roll to make sure the storm hadn't injured or killed workers.

As the rain pounded, investigators in wet suits assessed the damage.

"It was like a moonscape," Banaldo said, of the mud-covered road near the entrance.

Soldiers from Fort Carson's 52nd Engineer Battalion joined airmen from Peterson Air Force Base to start clearing debris and redirecting the deluge.

Keeping the facility operating is a top priority. Troops inside provide services including missile warning and missile defense.

The facility is designed to function for days with no connection to the outside world, but leaving it cut off by the slide wasn't an option.

At the same time, commanders had to ensure that the site kept its high level of security. The use of lethal force has been authorized to protect the place since it opened.

"We reconfigured security since we had part of our fence taken out," Harsha said.

As the storm passed, more damage became evident.

Years worth of erosion took place in hours.

A drainage pond downhill from the entrance, dry before the storm, filled with more than 15 feet of water.

Since the flood, the Air Force has taken emergency steps to clean up the mess.

A contractor that the Air Force kept on call for emergencies has moved in with mining equipment to clear debris. Tons of rock have been placed to reinforce NORAD Road.

Commanders hope to have most of the damage fixed before the snow flies.

Banaldo said the cost of the emergency repairs is still being calculated.

Next, the Air Force is pondering a problem that's facing much of the region: How to engineer its facility to withstand extreme weather described by some as "biblical."

"We're going through that process," Banaldo said.

No fix would be able to deal with a repeat of the epic storm. But repairs for the mountain facility that will last decades are a top Air Force priority, Harsha said.