San Joaquin Mtn is the highest point along a 25mi stretch of the Sierra crest in the Mammoth area between Mt. Davis to the north and an unnamed peak near Red Slate Mtn to the south. And yet it goes mostly unnoticed by tens of thousands of visitors that view it from US395 each year. Partly this is because it is dominated by the fantastically serrated Minaret Range which rises higher to the west, and partly because it hardly stands out along the more gentle ridgeline between the Mammoth Mtn and June Mtn ski areas. But those two detractions to the peak also provide the reason to go climb it - the elevation grade is the mildest for any peak in the Mammoth area, and the views of the Minarets along the entire route starting from Minaret Summit are outstanding. One does not even need to climb to the peak to enjoy the best views - simply hike out as far as you like and return for a splendid scenic tour of the area.
San Joaquin Mtn and the ridgeline it occupies run along the boundary of the Ansel Adams Wilderness. The west side is protected Wilderness, the east side lies in the Inyo National Forest. Snowmobiles in winter and 4x4 vehicles at other times are not uncommon sights. The owner of the two ski resorts has been petitioning for years to connect the resorts with additional ski lifts and runs along this ridge to make it the longest continuously serviced ski terrain in the US. If allowed, this would likely lead to development of the Glass Creek / Deadman Creek watersheds and a significant increases to both the year-round and seasonal populations. Frightening to environmental factions, a boon to development interests. Pick your side of the coming battle...
The peak can be climbed from either the June Lake or Mammoth areas. Though the peak is closer to SR158 and the town of June Lake, that approach requires nearly 2,000ft more elevation gain and is seldom used. Both TH directions are described here.
From the town of Mammoth Lakes, take SR203 up to the main lodge of Mammoth Mtn. Continue up to the pass (called Minaret Summit, oddly enough) where there is a large day use parking lot. Access beyond Minaret Summit is restricted and during daylight hours you are generally required to ride the shuttle bus to reach points west towards Devils Postpile. Another nice thing about this peak is you don't have to hassle with the shuttle and can drive to the trailhead any time of day.
North approach: from the June Lake turnoff on US395 (12mi south of Lee Vining), take SR158 west for about 5.4mi to an unpaved road marked only by the sign Yost Creek Trail. Turn left and drive a tenth of a mile to the trailhead parking. This is the trailhead for Fern/Yost Lakes, also used to reach the summit of picturesque Carson Peak overlooking the town of June Lake.
Others have also used the Rush Creek TH to reach San Joaquin Mtn, but not usually for dayhikes. The Rush Creek TH is located on the NW side of Silver Lake along SR158.
The summit can be climbed year-round, though most often in summer/fall. In winter, the easiest approach starts from the large parking lot at the main lodge for Mammoth Mtn. Snowmobiles provide the quickest winter access, and their tracks can be handy to follow after fresh snows have fallen.
Camping is allowed in most places in the surrounding Ansel Adams Wilderness and Inyo National Forest. Parties have camped at the summit and along the ridge, often near Dead Man Pass. The hike from Minaret summit is not particularly arduous and is most often done as a dayhike.
"Gabriel Moraga named the river in 1805 or 1806 for San Joaquin (Saint Joachim), the father of the Virgin Mary. (Arch. MSB, vol. 4, Munoz, Sept. 24, 1806.) The name spread up the river into the mountains, where it became North, Middle, and South forks. The mountain probably was named by the USGS during the 1898-99 survey for the Mt. Lyell 30' map, simply because it was a convenient name to borrow for a triangulation point. It is on the first edition, 1901." - Peter Browning, Place Names of the Sierra Nevada
"Crespi saw the river on Mar. 30, 1772, when he and Fages were attempting to reach Point Reyes, and he named it San Francisco for St. Francis of Assisi. Gabriel Moraga gave the name San Joaquin to the river when he reached its southern part in 1805-6, according to Padre Munoz's diary. Before and after Moraga's visit, various sections of the river had different names. However, in the records after 1810, San Joaquin is mentioned as if it were a well-known name. The name appears for the upper course of the river on Estudillo's map of 1819, and three main channels of the lower course are shown with this name on the Plano topografico de la Mision de San Jose (about 1824). The accounts of Kotzebue, Beechey, and Wilkes allow no doubt about the river's identity. On Narvaez's Plano of 1830, to be sure, the San Joaquin Valley is shown covered by an enormous swamp, Cienegas o Tulares. The maps of Wilkes (1841) and Fremnt-Preuss (1845) definitely identify the name with the major part of the river. The former has San Joachim, but Fremont uses the Spanish version. The county is one of the original twenty-seven, created and named on Feb. 18, 1850. A San Joachin City existed in 1850 (San Francisco Alta California, Feb. 7, 1850), but it soon vanished. The name San Joaquin Valley seems to have come into general use at the time of the Pacific Railroad Survey, 1853-54. The bridge across the river was built by the Central Pacific in 1869, and the station was named San Joaquin Bridge (Mary Seamonds)." - Erwin G. Gudde, California Place Names