Most people look out their back windows and, beyond the fence, can see into their neighbor’s kitchen or family room or bedrooms.

 Not true for folks in Oak Valley Ranch, a neighborhood tucked in the foothills between Mountain Shadows and Peregrine on Colorado Springs‘ northwest edge.

 Especially for families living on Front Royal, Coldwater and Hollandale drives.

 They back up to Castle Concrete Co.’s  Pikeview Quarry. Above is a 2001 photo of the quarry from The Gazette’s archives.

 We’re not talking Fred Flintstone here, either. This is the real thing, visible for miles along Interstate 25, just south of the Air Force Academy.

Lately, Oak Valley Ranch residents have had front-row seats for dramatic landslides that have sent upwards of 2 million tons of limestone cascading down the mountainside.

 The first slide occured Dec. 2, 2008, and dumped and estimated 1.5 million tons of limestone into the pit at the base of the cliff. The slide is obvious in the photo, above, taken the same day by The Gazette’s Carol Lawrence.

 But the mountain wasn’t done rockin’ and rollin’ yet. It let loose again Sept. 13 with a blast that sounded like thunder to neighbors who ran from their homes and ate dinner on their patios, watching as boulders the size of locomotives plunged down the cliff, dropping another 250,000 tons before it was done. 

Here’s a look at the two slides.

 Reader Chris Dorry posted on YouTube video of the slide that you can watch it on this link. At about the two minute mark, you’ll actually see landslide activity as rock breaks off and rolls. My friends at KOAA TV NewsFirst 5 also got some nice footage you can view here.

Here’s another cool video clip  that gives a great view of the landslide.

Here’s a photo of the action captured by neighbor Rob Hellem, who heard what he described as “rolling thunder” during dinner around 6 p.m. and looked out to see all heck breaking loose.

Experts say they expect further movement in the quarry.

M.L. “Mac” Shafer is vice president of Transit Mix Aggregates, which owns Castle Concrete and the Pikeview Quarry - a complex of about 100-mineable acres on a 190-acre tract.

 Transit Mix owned the Queens Quarry above the Garden of the Gods, which operated from about 1955 to 1989 and now has been reclaimed. The company also operates the Black Canyon Quarry behind Cedar Heights. And it has a sand mine along South Academy Boulevard.

Castle Concrete bought the Pikeview in 1969. It was operated for years by Peter Kiewit and Sons, Shafer said. It’s now known as Kiewit Western Corp.

Shafer said geologists agree that more landslides will occur. He said the limestone on the surface of the mountain sits on a layer of clay attached to the decomposed granite base that makes up Pikes Peak and much of the Front Range.

A year of steady snow and rain has saturated the limestone, coupled with the freeze-thaw cycle, caused it to slide, Shafer said.

On Feb. 12, federal Mine Safety and Health Administration officials issued five citations to Transit Mix and fined the company $2,564 for safety violations in connection with the slide. Shafer said the officials accused the company of mining too much of the base of the mountain, causing it to become unstable.

Since then, the company has been limited to removing its stockpiles of crushed limestone. The mine became more of a classroom for geologists and other scientists from around the world who have come to study the landslide.

After the Sept. 13 landslide, the mine has been shut down. Most of the stockpiles are exhausted. The conveyors of the rock crushers are sunning beds for bobcats. Deer and other wildlife are the only thing moving about in the mine.

Sophisticated laser sensors watch the mountainside, measuring it every few hours for any movement. Shafer said the company is developing a plan it hopes to present next June for possibly reopening the mine and finishing reclamation efforts.

Neighbors, meanwhile, are wondering if there’s any danger in rocks rolling into their backyards. Look at these bad boys hanging from the top of the latest slide. Shafer estimates the larger boulder on the right weighs at 20,000 tons! Like a locomotive perched on the mountainside.

Shafer said such a disaster is not likely. Below is a look at the mine, prior to the landslides, from GoogleEarth. It shows the pit.

For now, things are calm again. But, eventually, experts expect the mine to break loose again. They are especially watching a fault at the apex of the mine above the most recent slide. On a recent hike with a geologist, Shafer said he was able to actually look into the fault and see the spot where the limestone, clay and granite meet.

For now, the landslide have not destroyed all the reclamation efforts done over the past decade on the southern rim of the mine. More than 2,000 trees have been planted on the ledges of the mine by volunteers with the Colorado Mountain Reclamation Foundation.