An avalanche off Highlands Ridge over the weekend deposited tons of snow in Conundrum Creek Valley, snapped hundreds of mature trees and threatened a house.

“This is as big of an avalanche as this terrain can produce,” said Brian Lazar, deputy director of the Colorado Avalanche Information Center. “This is a landscape-changing event.”

The avalanche broke over a mile wide and ran more than 3,000 vertical feet downhill, CAIC estimated from aerial observations. Lazar said it started just outside the boundary of Aspen Highlands ski area.

The slide went down two popular backcountry ski routes off Highlands Ridge — K Chutes and Five Fingers. It likely slid across the vast area all at once, Lazar said. Officials believe it was a natural releasing avalanche that occurred sometime late Friday or early Saturday.

“This is a landscape-changing event.” — Brian Lazar, Colorado Avalanche Information Center

The snow and debris fell with such force that it kept going once it hit the valley floor, traveling a couple hundred feet up the east slope and then spilling downvalley.

A house at the end of Conundrum Creek Road sustained damage from the slide but was spared from obliteration by an avalanche retaining wall built in the shape of a protective wedge. The chimney was knocked askew and fir and aspen trees planted outside were snapped off and bent over from the force of the snow. The house is about 7 miles southwest of Aspen.

A property manager was checking the condition of the home Sunday afternoon and said the owners were not in town at the time of the avalanche.

The avalanche decimated the trailhead for the Conundrum Valley Trail, a popular route to Conundrum Hot Springs. The parking area used to be surrounded by trees. Not anymore.

“The Conundrum trailhead as we know it is gone,” said Glen Horn, a resident of Little Annie Road on the east side of Castle Creek Valley. He visited the Conundrum site Saturday.

“I’ve lived (in Little Annie) since 1985 and it’s the biggest avalanche I’ve seen,” he said.

Lazar said there have been numerous large slides throughout the Colorado mountains after a prodigious storm cycle. In the Aspen zone, the storm dumped 5 feet of wet, heavy snow and produced about 5 inches of water equivalency, according to CAIC.

“Slopes such as Highlands Ridge simply hit a breaking point with so much snow,” Lazar said.

CAIC’s discussion of avalanche conditions Sunday summed it up this way: “Overloading an already deep snowpack by increasing the season’s snow water equivalency by 25 percent is apparently how you create landscape-changing avalanches.”

The slide buried a long stretch of Conundrum Creek but it was flowing near the confluence with Castle Creek on Sunday.

The Five Fingers/K Chutes slide dwarfed the avalanche that covered Castle Creek Road at mile marker 4 on Friday night or Saturday morning. Deep snow sloughed off the steep road bank and buried the road in several feet of snow. It was reported by a technician for Holy Cross Energy who was responding to a report of a power outage in Conundrum Creek Valley. The road was fully opened by 8 p.m. Saturday.

Officials from CAIC surveyed the Castle Creek Road corridor from a helicopter Saturday. They decided with the help of a snow safety officer with Aspen Skiing Co. who lives in the neighborhood what areas should be targeted with explosive charges to try to trigger avalanches. Lazar said the intent was preventing larger, natural slides that could cover the road and threaten utilities. A firm called Telluride Helitrax was enlisted to drop 10 15-pound explosive charges on avalanche paths, according to a news release from Pitkin County. No slides were triggered, Lazar said.

A slide out of Maroon Bowl into the Maroon Creek Valley floor temporarily plugged the creek at the beginning of the storm cycle, Lazar said. The blockage affected the city of Aspen’s water intake for a short time. City officials were concerned that a slide in Castle Creek Valley would plug that creek as well. It is another intake for the municipal water system. Lazar said the slide that blocked Castle Creek Road temporarily plugged the creek, but it soon flushed through the snow.

The avalanche danger for the Aspen zone remained at “high,” or a level 4 out of 5, on Sunday and CAIC issued an avalanche warning.

“We wanted to go at least one day without a landscape-changing event” before easing the warning, Lazar said.

Even when the rating decreases to considerable, the size of the avalanches will undoubtedly kill a person, he said.

scondon@aspentimes.com