As part of a trail reconstruction project at the Alluvial Fan in Rocky Mountain National Park, a new bridge was laid across the Roaring River, which flows through the boulder field left by a 1982 flood and descends from right to left. The new trail opened Sept. 25. (John Meyer, The Denver Post)

With more than 350 miles of trails, 30 miles of the Continental Divide and more than 50 peaks jutting above 12,000 feet — including Longs Peak, the 14,259-foot monarch of the Front Range — Rocky Mountain National Park abounds with spectacular adventures for hard-core mountaineers and uber-athletes.

The popular Alluvial Fan area stands in a different category, though, because it offers huge scenic payoffs with easy accessibility for all, including visitors in wheelchairs. The trail across a massive boulder field is less than half a mile long with an elevation gain of only 56 to 63 feet, depending on whether one starts from the east or west side. It was closed this summer for a trail reconstruction project that took more than a year to complete and re-opened Friday.

The Alluvial Fan didn’t even exist until 1982, when a manmade dam 6 miles up the Roaring River failed, sending huge rocks and boulders crashing down the valley and leaving a massive pile of them at the bottom — the Alluvial Fan. Jesse Miller, the park’s trails supervisor, was camping up near the dam the day it broke.

If you go

Enter Rocky Mountain National Park at the Fall River Entrance (U.S. 34). Follow Fall River Road to Old Fall River Road/Endovalley Road and turn right. The Alluvial Fan area will be on your right, about a half mile up that road. NOTE: Until Oct. 13, reservations are required to enter the park from 6 a.m. until 5 p.m.

“It was a scary experience,” Miller said. “Hiking down, it sounded like a bowling alley, giant boulders crashing into each other, trees coming down.”

The Alluvial Fan became a popular tourist attraction because of the stunning size of the boulder field. A trail was built across it in 1985, including a short bridge over the Roaring River. Visitors marveled at the power of water and gravity to move two-ton boulders as much as 6 miles, dropping them nearly 2,500 feet in elevation.

Then came the great Front Range Flood of 2013, when a cold front fed by monsoonal moisture stalled over the area, dropping up to 16 inches of rain in places and creating widespread flooding that isolated the town of Lyons. One of those floods came gushing down the Roaring River.

“The 2013 flood wiped out the whole infrastructure that had been built after the ’82 flood,” said Kyle Patterson, the park’s public affairs officer. “We received 12, 14 inches in a 24-hour period.”

A flood in 2013 caused by a massive rainstorm that dropped 12-14 inches of rain in Rocky Mountain National Park left up to 15 feet of sediment at the Alluvial Fan. Park officials decided to leave this sign as it was to show the depth of that deposition. (John Meyer, The Denver Post)

That flood broke up the old asphalt trail, washed out the bridge and deposited up to 15 feet of sediment in places. For years, visitors were left to admire the scene from a distance or access it via rock-hopping.

Then, 3 years ago, a plan was announced to rebuild the trail, which required environmental assessments and complicated engineering. Construction began last year.

The trail surface is made of FilterPave, which feels solid underfoot — sort of like a backyard patio floor — but is porous to allow for drainage.

“The really cool thing about this is it’s a hardened tread so it’s a very firm surface for someone in a wheelchair, but it’s also porous, so water runs through it,” Miller said.

The trail meets the criteria of the federal Architectural Barriers Act and it is designated as an Outdoor Recreation Accessibility Route.

The Alluvial Fan boulder field in Rocky Mountain National Park was deposited in 1982 when a dam failed 6 miles up the Roaring River, sending rocks and boulders tumbling down 2,500 feet in elevation. It quickly became a popular place for park visitors and a trail was built across it in 1985, but it was destroyed by another flood in 2013. A new trail opened Friday Sept. 25. A waterfall can be seen at the center of the photo. (John Meyer, The Denver Post)

“This is the biggest front-country (trail) project we’ve taken on since I started here in 2003, and probably is the biggest since they did the improvement at Bear Lake in the late ’90s,” said Doug Parker, the park’s trails program supervisor, who was with Miller that frightening night in 1982 when the dam failed. “One thing I think they did really well (is) the way the trail is lined (with rocks). It doesn’t look manufactured, it’s built to look like the environment, rough and inconsistent. They did a really nice job of blending in the aesthetics of the trail with the outside environment.”

“Something else they did I think was really cool, they set some rocks higher — we call them grandpa rocks,” Miller said. “So grandma or grandpa, if they wanted to stop, could sit down there and still have a really nice view.”

And those views are great. Above the trail there is a waterfall. Down below is the wide valley of Horseshoe Park, and on the opposite side of the valley, Hidden Valley with portions of Trail Ridge Road visible high above.

There are parking lots on the east and west sides of the trail. The west side includes restrooms and a picnic area.

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