Located 6.4 miles northwest of Pagosa Springs, Upper Rim Trail begins at Gate 5, which is one of the most popular routes in the area because it's short, accessible, and offers great views of Martinez Canyon.  If you do the loop clockwise, you'll spend the first 1.5 miles paralleling the scenic, rocky edge of the canyon rim, with glimpses of the cottonwood-lined creek 100 feet below.  This section of trail is mostly downhill and is covered with blocky sandstone chunks, which offer many ankle-twisting opportunities.  The trail turns northwest and follows the rim of a tributary canyon, climbing to a trail junction at mile 2.3.  Stay right on the Upper Rim Trail and continue climbing on this smoother section of trail through the ponderosa pine.  At mile 3.7, take a right at the junction with Newt Jack Trail and descend back to the trailhead to complete the 4-mile loop.  Because it's mostly south-facing, Upper Rim is one of the 1st trails to dry out in the spring (it's usually mostly dry by mid April).