-Trailhead: Borrego Trailhead. This trailhead is signed. Reached using Forest Road 306.
- Distance (one way) to reach Peak 11821: 12.1 miles, elevation gain of almost 6000 ft. Sierra Mosca is 1.5 miles away.
- Trails: Borrego Trail #150 (signed), Sierra Mosca Trail #156 (signed), Agua Sarca Trail. The Borrego Trail gets you to the Sierra Mosca Trail. The Sierra Mosca Trail goes to the summit ridge of Peak 11821 where it meets the Agua Sarca Trail. The Agua Sarca goes near the summit of Peak 11821 and near the summit of Sierra Mosca. Both peaks require leaving the trail to reach the highpoint. Any other trails you see on a map going up/down Sierra Mosca no longer exist. Expect to bushwhack down unless you reverse direction and return the way you came. The bushwhack down off Sierra Mosca to the Sierra Mosca trail is steep, about 1100 feet drop in elevation.
- General Issues: Some deadfall, overgrown and non-existent trails, and the current trail does not follow the map location in some places. The trails to the summit of both peaks have very little deadfall. A logging crew was working a nasty section of the Sierra Mosca trail that follows the Rito Con Agua the day I was returning so those barriers will no longer exist. At higher elevations the trail fades away and cairns mark the route but its a bit of hit and miss.
- Water: Rio Medio and the Rito Con Agua (below 8800 feet). There's also a nice stream on the mountain at 10600 ft (N35.9219, W105.7569). The Sierra Mosca trail crosses this stream. Consideration: 2020 is a drought year.

There is no easy way to get to Peak 11821 or Sierra Mosca. Its made even worse by topo maps which do not reflect current trails leading to these mountains. For example if you look at the 2016 forest service map you will see the Sierra Mosca trail starts near the village of Cundiyo. NO!!! That area is private land and there is no access. So you must start at either the Borrego Trailhead or at the southern end of the Borrego Trail. I chose to start from the northern end of the Borrego Trail, Trail #150. To get to it you turn off NM-503 (North of Cundiyo) onto FR-306. FR-306 does have a sign but its only partially visible. You go down a dirt/gravel road for about 6.8 miles to a road on the right that is signed "Borrego Trail". Its only about a half mile to a small parking lot next to a wooden sign board. The trail starts right next to and behind the sign board, following an old road to a sign marking, Borrego Trail. The trail descends about 700 feet down to the Rio Medio which requires fording. Trail #150 is easy to follow and slowly gains altitude as you make your way to the junction with the Sierra Mosca trail (signed). The Sierra Mosca trail follows the Rito con Agua stream which runs until you reach about 8800 feet then it disappears. For most of the way, the trail is obvious and follows the northern side of the stream although it does switch back and forth about five or six times. Eventually it starts climbing out of the drainage. At about 9600 feet the trail hits a ridge line with a nice meadow. I spent the night there. No water so you have to haul it up. At around 10700 ft the trail hits a meadow. Look for a large rock cairn. From that point on until you reach the summit ridge of Peak 11821 its primarily navigation from cairn to cairn. The trail eventually becomes obvious as you make your way to Sierra Mosca. The Agua Sarca trail seems to bypass the summit, heading southwest, so I left the trail and bushwhacked to the summit. Maps show the Rio Molino trail #227 heading down off Sierra Mosca towards the Sierra Mosca trail. NOPE, doesn't exist. It's a steep mile long bushwhack down to the Sierra Mosca trail.