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UN 12100 "X Prime"

UN 12100 "X Prime"

UN 12100 "X Prime"

Page Type: Mountain/Rock

Location: Colorado, United States, North America

Lat/Lon: 39.37420°N / 105.6185°W

Object Title: UN 12100 "X Prime"

County: Park

Activities: Hiking

Season: Spring, Summer, Fall, Winter

Elevation: 12100 ft / 3688 m


Page By: Sarah Simon

Created/Edited: Nov 5, 2011 / Nov 5, 2011

Object ID: 758218

Hits: 1890 

Page Score: 83.1%  - 16 Votes 

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Approaching the  X Prime  summit
Approaching the "X Prime" summit

Official USGS summit names are hard to come by in the Kenosha Mountains. Indeed, along the entire primary ridgeline running from UN 12100 “Kenosha Peak” on southward, none of these gnarled, granite-topped mountains lays claim to a formal title. Thus we have another UN 12100, nicknamed “X Prime.”

Little companion to UN 12429 (“Peak X”) to the southeast, “X Prime” is marked by the characteristic Kenosha Mountain appearance: Densely forested lower slopes, broad tree-less upper slopes, all topped by a gnarly, wart-covered head of weathered granite.

Colorado Rank: Soft ranked peak*
Prominence: 280 feet
USGS Quad: Topaz Mountain
Planning Map: Trails Illustrated #105 Tarryall Mountains/Kenosha Pass

Rank & Prominence Source: Lists of John

*In a nutshell, soft ranked peaks lacks 300 feet of confirmed gain from the saddle with their highest neighbor. However, if their optimistic prominence proves true, they would be ranked peaks. But let’s not get bogged down in the details here.

Getting There

Looking back at  Peak X
Looking back at "Peak X"

Bounded by US Hwy 285 to the north and Park County 77 to the south, “Peak X” is an accessible peak.


North Ben Tyler Trailhead: Follow Hwy 285 6.8 miles west of Bailey. Trailhead will be on the left (south) side of the highway and parking is limited.

Payne Creek Brookside Trailhead: From Hwy 285 in Bailey, cross the South Platte River on CR 64. Stay left at a fork in the road after about ½ mile, and drive about 2.2 miles to the rrailhead on the south side of the road.

Taking in the scenery from the saddle
Taking in the scenery from the saddle


Long Gulch Trailhead: The trailhead closest to the peak is the Long Gulch Trailhead, reached via the graded dirt Long Gulch Road (CR 39 / FSR 39). From Hwy 285 at the town of Jefferson, turn right onto CR 56 and travel about 10 miles. The trailhead is at the end of a short spur road on your left (north side of the road).

North Fork Trailhead: From Hwy 285 at the town of Jefferson, turn right onto CR 56 and travel about 17 miles. Turn left onto FR 134 (high clearance required).

South Ben Tyler Trailhead: From US 285, go 7.3 miles on the Lost Park Road (County Road 56) to Forest Road 133. Go left (north) 1 mile to Rock Creek Trailhead. You can also continue 1 mile further to a second, smaller trailhead on the Ben Tyler trail. Road is narrow and rough, and parking is very limited.

Views from the Summit

Views from the summit - Evans Group close-up
Evans Group close-up
Views from the summit - toward Evans Group
Toward the Evans Group
Views from the summit - Mosquito Range
Mosquito Range
Views from the summit - toward Guanella Pass
Toward Guanella Pass

Red Tape

Descending  X Prime
Descending "X Prime"
Snow descent,  X Prime
Snow descent, "X Prime"

There exists little or no red tape in this part of the National Forest, but note that “X Prime” is protected within the wonderful Lost Creek Wilderness. Please follow LNT (Leave No Trace) principals:
1. Plan Ahead and Prepare
2. Travel and Camp on Durable Surfaces
3. Dispose of Waste Properly
4. Leave What You Find
5. Minimize Campfire Impacts
6. Respect Wildlife
7. Be Considerate of Other Visitors


The unfortunate one
The unfortunate one

Lost Park (FR 56) and Rock Creek Hills (FR 39) about in undeveloped Forest Service camping. These sites are available on a first-come, first-served basis. Many are dry (you need to haul your own water) and the sites are in high demand during the summer high season.

Weather & Seasons

 X Prime  summit jar
"X Prime" summit jar
“X-Prime” is an excellent year round mountain, but check conditions in snow season regarding whether or not access roads are passable. Access to this peak via dirt Forest Service roads will be hampered by heavy snows, lengthening your approach to this summit. The access roads in this area melt out earlier and get snowed-in later than many higher-altitude, heavier-snowpack climbing areas in Colorado.

That being said, if you want solitude for the entirety of your hike, visit this peak in snow season. Summer brings heavy, heavy crowds to the Lost Park area in particular. Campsites are at a premium in the warmer months, traffic is thick, motorized recreation is heavy and other visitors swarm the dirt roads.
Click for Jefferson, Colorado Forecast


Approaching the "X Prime" summitUN 12100 "X Prime"The unfortunate oneViews from the summit - toward Evans GroupViews from the summit - Evans Group close-upLooking back at "Peak X"Snow descent, "X Prime"
Descending "X Prime"Taking in the scenery from the saddle"X Prime" summit jarViews from the summit - toward Guanella PassViews from the summit - Mosquito Range