The trail starts at the Montville Trailhead that is located between the visitor center and the Pinyon Flats Campground, which is the only campground that accepts reservations in the park. The trail for Mosca Pass splits after only a few hundred feet from the Montville Trail. The biggest attraction for this trail is the incredible variety of wildflowers that bloom, as many as 50 different species.
This hike is one of the few accessible trails into the Sangre de Cristo Mountains that doesn't require a vehicle with four-wheel drive. It is a nice alternative to being on the sand dunes, especially in the afternoon during the summer when the dunes can reach temperatures as high as 140 degrees. Unfortunately, the end of the hike is somewhat anti-climatic: an open grassy field that doesn't provide great views. This is also one of the very few trails in the national parks that allows dogs, though they must be kept on a leash no longer than 6 feet.
The trail meanders through dense woods and beautiful meadows alongside Mosca Creek, though it does take you to a few cliffs where you are able to get partial views of the sand dunes. Most of the views are of the surrounding forest and mountain. The trail winds farther into the mountain, so the best views of the dunes are early on in the hike. Though you do gain 1,500 feet in elevation, it isn't steep, and it's a gradual gain throughout the hike. This is also a great hike to escape the crowds in the park and its main attraction, the sand dunes. If hiking in the summer, make sure to bring bug spray and expect to encounter mosquitoes.