What are the Mormon Trail and Hidden Valley?
Hidden Valley is the one South Mountain hike people recommend to each other, and the Mormon Trail is the fast way in. From a small lot at the end of 24th Street the trail climbs 1.1 miles and 720 feet up the north face of the range on rocky switchbacks, past a few panels of Hohokam petroglyphs pecked into the dark varnish beside the path, to the National Trail on the crest. From there a short walk and a right turn drops you into Hidden Valley, a flat-floored bowl of pale granite tucked behind the ridge.
Its half-mile trail threads the Natural Tunnel, a short passage under stacked boulders, follows a sandy wash to a naturally smooth rock slide that generations of kids have polished further, and exits through Fat Man’s Pass, a slot between house-sized boulders that adults negotiate sideways with packs off. The Mormon Loop Trail takes you back around to the Mormon Trail and down. The whole thing is about 3.7 to 3.9 miles with roughly 850 feet of total climbing, which puts it between Tom’s Thumb and the Hieroglyphic Trail for effort and ahead of both for sheer fun with children.
It is also one of the busiest trails in South Mountain Park, which the city acknowledges by asking mountain bikers, who are technically allowed, to stay off it. What you get is the most entertaining two hours of hiking in the Phoenix city parks. What you do not get is water, shade, a reliable restroom or a quiet trail on a winter Saturday.
How to hike Hidden Valley right
Get there. Take Scottsdale Road south to Loop 202 west, then I-10 west to Baseline Road. Go west on Baseline to 24th Street and south about a mile and a half until the road ends at the trailhead, 8610 S. 24th St. It is about 28 minutes from Old Town without traffic.
Park early. The lot is small, free, and open 5 a.m. to 7 p.m.; the trails stay open till 11, but the car does not. It holds a few dozen cars, fills early on cool-season weekends, and the streets around it are residential with no sanctioned overflow. Start by seven. If it is full, drive east to Pima Canyon (4500 E. Pima Canyon Rd.) and do the longer version, or come back on a weekday.
Bring everything. No water, no shade, no sure restroom; Pima Canyon has both if you need them. Two liters a person once the weather turns in April; this is a bare granite mountain with a south-facing return leg.
Pick the season. October through April. The climb faces north and holds shade until mid-morning in winter and early spring, which is the only reason this works as a late-morning hike in January. From May through September, be on the trail at first light and down by nine; the summer rules apply.
Walk the loop clockwise. Climb the Mormon Trail, turn left on the National Trail and take the first right onto the Hidden Valley Trail so you hit the Natural Tunnel first and finish at Fat Man’s Pass with the rock slide as your reward, then return on the Mormon Loop. Clockwise means you climb the loose Mormon Loop grade instead of descending it. Most people finish in two to two and a half hours.
The pass is a real squeeze. Fat Man’s Pass is narrow enough that large adults and large dogs turn around. Packs off, go sideways, and send a child through first to prove it works. Expect a short queue on a winter Saturday. The rock slide is fun and will shred thin pants.
Leave the petroglyphs alone. They are a few steps off the Mormon Trail and have survived a century of Phoenix. Do not touch them, climb them or add to them; the varnish does not come back.
Dogs. Allowed on leash, but the pass and the tunnel are awkward for anything larger than a beagle. Phoenix bans dogs on all city trails at 100 degrees or more.
Skip it if you want quiet or a gentler grade. Javelina Canyon is the east end’s empty door, and Pima Canyon reaches Hidden Valley in about 6 miles at an easier slope.
The valley a newspaper saved and the CCC built a road to
The rock art came first. For roughly a thousand years the Hohokam, who dug the canals that watered the Salt River valley below, climbed into this range and pecked figures into its varnished boulders, and the north-side trails out of 24th Street pass some of the densest panels in the park. Their descendants, the Akimel O’odham, and the Piipaash still hold the land along the mountain’s south side in the Gila River Indian Community. To the settlers of early Phoenix the range was simply the Salt River Mountains, a dry ridge on the far side of the river.
It became a park because a newspaper owner decided it should be. In 1920 Dwight B. Heard, a rancher who owned the state’s largest newspaper, began using its pages to push for preserving the range, and a city committee took up the cause. In June 1924 President Calvin Coolidge approved the sale of the first 13,000 acres of federal land to the city for $17,000, about $1.25 an acre. The city called it Phoenix Mountain Park before settling on South Mountain. Without Heard, as Arizona Highways put it, Hidden Valley would likely be a subdivision.
The trails came with the Depression. Between 1933 and 1940, more than 4,000 Civilian Conservation Corps men from two camps at the mountain built most of the park’s roads, ramadas, stone buildings and trails, including the ridge route now called the National Trail that the Mormon Trail climbs to meet. CCC trails were built to last, and the stonework along the crest is still carrying traffic nearly a century later.
The name is the part nobody can explain. We found no reliable source for why the trail from 24th Street is called the Mormon Trail; some writers tie it loosely to Latter-day Saint settlement in the Salt River valley, but nothing documents it, so treat any story you hear as a story. What is clear is how the trailhead got so busy. Bond programs in the 1970s and 1980s grew the park to 16,283 acres, and the neighborhoods north of Baseline filled in right to the foot of the mountain, which turned a dead-end street into one of the most-used doors in the park.
Lately the pressure has only grown. The park marked its centennial in 2024, the South Mountain Freeway opened along its western foothills in 2019, and the Mormon lot, with no overflow and neighbors who notice, is now the practical limit on how many people walk through Fat Man’s Pass on a winter morning.
Why it matters
South Mountain is the reason Phoenix has one of the largest city parks in the country, and Hidden Valley shows why people fought for it: a granite hideaway, a tunnel and a slot between boulders, a few hundred feet above a city of millions. The Mormon Trail adds the two other layers of the story, Hohokam rock art on the way up and CCC stonework on the crest. It is a short, honest climb with a payoff children remember. For a Scottsdale visitor the verdict is plain: half an hour from Old Town, free, and worth an early alarm on any cool-season weekend. Park by seven, go clockwise, and take your pack off before the pass.