Community members will encounter closures at popular Boulder trails and trailheads this year while the City of Boulder conducts numerous maintenance and repair projects. Many trail projects will occur along older “legacy” mountain trails – which are often steep and prone to erosion, requiring ongoing maintenance.

City of Boulder Open Space and Mountain Parks (OSMP) highly encourages community members to visit OSMPTrails.org to see trail closures that will be in place for the following projects:

  • Royal Arch Trail: Starting as early as Wednesday, May 25, OSMP will close the trail to resume maintenance work along the popular Boulder trail. This year, OSMP trail crews will focus on rebuilding steps along Sentinel Pass, which leads to the “Royal Arch” formation. Trail crews will use materials that a helicopter delivered to the site in the fall of 2021. While this work occurs, the full length of the trail will be closed from 8 a.m. to 4:30 p.m. Monday through Thursday – with occasional closures from 8 a.m. to 4:30 p.m. on Friday. These closures will be in place through the summer and into the fall.
  • Mount Sanitas Trail: Beginning in July, OSMP staff and conservation corps crews will continue trail maintenance and native plant restoration along the trail. Visitors may encounter temporary closures in the fall when a helicopter moves construction and trail material into place.
  • 1st/2nd Flatiron: OSMP will continue work to repair the trail. Staff will rebuild stone structures and conduct native plant restoration. During the summer, the trail will be closed 8 a.m. to 4:30 p.m., Monday through Thursday. This trail closure will extend into the fall. The closure will start at the base of the 1st Flatiron. Climbers may climb the 1st and hike down the trail but may encounter significant delays.
  • Bear Canyon Trail: Trail construction has resumed. OSMP doesn’t anticipate long-term trail closures for this upcoming work. However, trail users may encounter intermittent delays while work occurs – most are anticipated to be brief 10-minute delays, though closures up to 1 to 2 days may be possible. OSMP’s construction work along the Bear Canyon Trail will re-reroute a one-third mile section of the path away from an ecologically important stream area to improve wildlife habitat and make the trail less prone to flood and erosion damage.
  • Flatirons Loop: Closures of the trail are expected to occur in the summer and through the fall. Over the years, OSMP has observed significant erosion and “braiding” along the trail – which occurs when visitors walk off trail, which can widen the tread. OSMP crews will install stone steps and improve the trail tread. OSMP will institute closures from 8 a.m. to 4:30 p.m., Monday through Thursday, while this work occurs.
  • Chautauqua Trail: This fall, OSMP will close the Chautauqua Trail to conduct “spot” repairs on Boulder’s most popular trail. This repair work will require multiple 24-hour closures.
  • Mallory Cave: An OSMP trail crew and the Front Range Climbing Stewards will repair eroded switchbacks and close undesignated trails. The trail will be closed for two days each week in October while this work occurs.

OSMP also will be closing one trailhead every Wednesday over the next two months to conduct parking lot maintenance and repair work. Review upcoming trailhead closures online. There will be longer closures at the Four Mile and Chapman Drive trailheads later this year.

OSMP recently reopened the Marshall Mesa Trailhead following the Marshall Fire. OSMP also reopened Marshall Mesa, Marshall Valley and Coal Seam trails. Portions of the Marshall Mesa Trailhead will remain closed until more extensive repairs are completed. On-trail-use-only regulations in the Marshall Mesa area will be enforced as the area has changed since the Marshall Fire and hazards may be present.

Visitors can also learn about muddy trail closures by texting "OSMP" to 888-777 and following @boulderosmp on Twitter and Facebook.