Observatory Rock, while only slightly over 10,000 feet, offers one of the best views in the Retirement Range. The Retirement Range is comprised of four groups of mountains: The Platte River Mountains, the Kenosha Mountains
, the Tarryall Mountains and the Puma Hills. Observatory Rock is in the northwest area of the Puma Hills and is located in Pike National Forest
just west of Tarryall Creek and the Lost Creek Wilderness
The reward for completing the steep 700'+/- scramble up the south slopes to the west ridge is quickly found with a fun Class 2+ scramble up the west summit gully. The final 15 feet or so of the gully could be called easy Class 3. The summit views are memorable.
The rock is rarely climbed with an average of about one or two entries per month in the summit log. The log was located near a USGS marker.
Observatory Rock is well covered in Gerry and Jennifer Roach's "Colorados's Lost Creek Wilderness - Classic Summit Hikes".
The Trails Illustrated Map #105 – Tarryall Mts. / Kenosha Pass would be very helpful in finding the trailhead and identifying surrounding peaks upon summiting.
FROM THE NORTH (DENVER):
Head west on US 285 passing over Kenosha Pass. Just over 4 miles west of the Pass turn south (left) on Park County 77 in the small community of Jefferson. Continue south on 77 until you come to the Tarryall Reservoir. Just south of the reservoir, turn right onto Forest Service Road (FSR) 23.
FROM THE SOUTH (COLORADO SPRINGS):
Head west on US 24 to the small community of Lake George. Shortly after crossing a young South Platte River, turn north (right) on Park County 77. Continue north on 77 until you come to the Tarryall Reservoir. Just south of the reservoir, turn left onto Forest Service Road (FSR) 23.
FSR 23 is passable to most vehicles although a high clearance vehicle would be best. After a few miles you will veer right onto FSR 146. Follow FSR 146 past the south side of Eagle Rock
. Eagle Rock is a great Class 2 scramble via it’s southwest ridge and a great warm-up for Observatory Rock. At less than two miles down FSR 146 you will turn right onto FSR 834 which is posted as a dead-end. Some folks in passenger cars may wish to park here and begin hiking. Observatory Rock is now quite obvious to the north.
FSR 834 first heads northeast down into Berkey Gulch. The road gradually turns north and then west. At about 2 miles from FSR 146 the road reaches the bottom of Swigler Gulch. At this point there are three choices. Left heads west up into Swigler Gulch. Right is a continuation of FSR 834. Straight leads up through a nice aspen forest to the base of Observatory Rock. Continue straight until you enter a clearing surrounded by aspen at the south base of the Rock. This is the trailhead.
The entire route is located in the Pike National Forest and requires no permits.
When To Climb
The access roads may not be passable in winter or after a heavy spring snow – check with the Forest Service. Parts of the summit gully may be dangerous with ice and or wet conditions.
There are several Forest Service Campgrounds located along Park County 77. To the south is the Spruce Grove and Twin Eagles Campgrounds. Packer Gulch Campground is located at Tarryall Reservoir along FSR 23.
There are some nice flat areas in the last half mile to the trailhead that show signs of dispersed camping.
Check local weather