Centennial Park Trailhead, Boulder, 16 miles from Longmont
Drive past the bustling and overflowing Sanitas Trailhead and arrive at the active but less frenetic Centennial Park Trailhead. Follow signs toward the Red Rocks Loop trail, a .5 mi trail that loops around a beautiful jutting rock formation with gorgeous views of the surrounding foothills and Boulder below. While the hike isn't long, it is steep at times with sandy, crumbling rocks. There are many other trails around this area, so you could extend your outing.
For more local hikes see here and here.
This is a late March day... Sunny and 70 degrees!