Neffs Canyon, and the shaft beneath it

Yes, on a leash. The Forest Service listing for Neffs Canyon Trail 456 states that leashed pets are permitted, and the reason is that this drainage is not inside the protected drinking water watershed. Dogs must also be under control at the trailhead and in the parking lot. This is not one of the canyons that runs an odd and even off leash system, and it is the opposite of Big and Little Cottonwood, where dogs are prohibited outright.

At the top of White Way, reached through the residential streets above Olympus Cove on the east side of the valley. Olympus Cove became part of Millcreek when the city incorporated in 2016, so the lot sits just over Holladay's northern boundary rather than inside the city, though for most Holladay addresses it is still about a ten minute drive. The lot is small, there are no facilities, and there is no public parking in the neighborhood below it.

The Forest Service publishes Neffs Canyon Trail 456 at 4.44 miles with about 1,821 feet of elevation gain, and notes no motorized use and that the route is not suitable for bikes or horses. That distance is the trail rather than the round trip. The path climbs east through scrub oak and maple on the shaded lower canyon and opens into meadow ground under the ridge, with no single destination that defines whether you finished it.

1,163 feet, revised down from a computed 1,186 feet when a party first reached the bottom of the main passage in 1956. That makes it one of the deepest caves in Utah and about the fifteenth deepest in the United States in published rankings. The entrance was found in 1949 by two teenage brothers, John and Jamie Lyon, out hiking in the canyon on the north side of Mount Olympus, and systematic exploration followed through the 1950s.

No, not as a visitor. The Forest Service closed the cave to the public on safety grounds many years ago, and access since then has been tightly restricted through the agency in coordination with the Salt Lake Grotto, the local caving group. Entering without Forest Service permission is a federal offense. It is a technical vertical system where a rescue would be a major operation, so treat it as a piece of local history rather than an objective, and do not go looking for the entrance.

The Neff family, who arrived with the 1847 pioneer companies. John Neff bought mill burrs from Brigham Young at Winter Quarters and had a flour mill running on the creek in the Mill Creek area by March 1848, the first in the valley to produce refined flour. Published sources differ on whether the canyon carries John's name or that of his son Franklin, and there is no settled answer, so the family rather than the individual is the honest attribution.

No, and confusing them is easy because they share a mountain and a family name. Mill Creek Canyon is a much larger canyon further north with a paved road up it, an entrance fee and a well known odd and even dog system. Neffs Canyon has no road, no fee and no facilities at all: it is a small trailhead at the end of a residential street opening onto a footpath, and it cuts into the north side of the Mount Olympus massif.

It is friendlier than the Mount Olympus trail on the front of the same mountain, mostly because there is no scramble and no single summit to feel obliged to reach. The lower canyon is shaded and the gradient is honest rather than brutal, and turning round in the meadows is a complete outing. What it is not is a stroll: there is no water, no restroom, no trash bin and no cell coverage inside the drainage, so go equipped for a real walk.

Spring through fall, with early fall probably the best of it: cool air, color in the oak and maple, and firm ground. Either side of that the lower canyon turns to mud and old snow. Summer works if you go early, because the lower slopes are warm dry rocky ground where rattlesnakes are perfectly at home and there is no water anywhere on the route. Cell coverage drops off once you are properly in the drainage.