You access it via the Loma Alta trailhead, which is at the north end of Camino Loma Alta. This north south road is accessed from East Spanish Trail. Either drive east on Broadway or 22nd to Spanish Trail, or if you live on the west side of town (like me), take I-10 to the Vail Wentworth exit and head north to Spanish trail.
From the trailhead take the trail to the east (actually an old road) for 2.3 miles of fairly uninteresting hiking to the Quilter Trail. At this point you have joined the AZT. 5.5 miles from here you will reach the old trail to Manning Camp. This trail begins at the old Madrona ranger station, which you cannot get to as it is behind private land in what is called the X-9 Ranch development. Another 2.9 miles will bring you to the Grass Shack area where you can camp if you have a permit. This is 10.7 miles all told from the trailhead. Water may (or may not) be available here.
You can continue another 5 miles to Manning camp and the summit area of Mica Mountain. Provided you don't mind 3000 feet of uphill hiking to boot. On 11-27-2020 I hiked this area with a 28 pound pack and found temperatures at Grass Shack fell to just below 29 degrees on a rather warm November day.
Tom's hiking pages / tom@mmto.org