Every area has its test pieces, and Boulder, Colorado, has many. One of the most tested is Mt. Sanitas, part of the City of Boulder Open Space and Mountain Parks (OSMP). In the history of the program, OSMP has only allowed one race on its property, and that was an ascent of the Mount Sanitas Trail, which gains 1300 feet over 1.4 miles. The "Cardiac Arete" race was held October 25, 2003, and was won by Nathan Schultz in 15m27s.
This FKT is from TH to peak - the generally accepted candidates to get from the TH to shadow canyon are mesa trail (with or without the recognized "mesa cutoff"), homestead trail, or towhee trail, but you're welcome to stick to any OSMP trails you like.
Bear is really a subsidiary summit of South Boulder Peak, but with a satisfying summit with terrific views. The standard route starts from the Cragmoor TH, at the west end of Cragmoor Road, and ascents the Cragmoor Connector, North Fork Shanahan and Fern Canyon trails to the true summit of Bear Peak, where there is a benchmark.
This route is in City of Boulder
This is a Premier Route (R2R2R). To claim an FKT on this route, you must meet a high standard of documentation and verification. See details here: https://fastestknowntime.com/premier-routes.
Nick Clark posted the route:
The trailhead for Round is 7 or 8 miles (maybe more) west of Loveland on Hwy 34. Two or 3 miles west of the Big Thompson Narrows, there is a pull-off to the left. This leads to the parking lot for Round. Route goes from trail map to big cairn at Summit: 4.8 miles & 3,000'. 95% singletrack.
Note: The Round Mountain Trail ascends Sheep Mountain (confusing!)
Towers Road, in the Horsetooth Mtn trail system, is a well-established Fort Collins time-trial route - mainly for mountain bikers, but also for trail runners.
This popular, hilly 11-mile loop is near Estes Park, CO. There is a Strava segment for the loop.
http://www.rockymountainhikingtrails.com/lumpy-ridge-loop.htm