LITMIR.BIZ

       The 45th parallel also passes through Minneapolis–Saint Paul, Nova Scotia, Bordeaux, the Black Sea, the Caspian Sea, Mongolia, and the northern tip of the Japanese islands.

       Logistics

      The Boiling River is generally open for soaking sunrise–sunset, or as late as 5 a.m.–9 p.m. in the high season. Check with the visitor center in Mammoth for the current status. Even though there are few signs, the area is one of the park’s worst-kept secrets and receives up to 200 visitors per day.

      Bring drinking water, hiking sandals (flip-flops will fall off in the river), and a towel, plus a flashlight if visiting around sunset. The only changing area is inside the restroom at the trailhead.

       Trail Description

      Stream

      From the far east side of the main parking area ▸1 on the east side of the North Entrance Road, a wide, flat gravel path heads upstream alongside the Gardner River (yes, the river and the town of Gardiner are spelled differently, for no good reason except that Montana is quirky) for about half a mile.

       OPTIONS

       Mammoth Campground Trail

      If you are staying at Mammoth Campground, it’s worth knowing that an alternative path, which is roughly as long as the trail from the parking lot but much steeper, descends 250 feet in elevation from the far northeastern corner of the camping area. The unsigned trailhead is across the North Entrance Road, to the left of the prominent Dude Hill, but there’s no parking here. It’s not uncommon to confuse this route with the signed Lava Creek Trail that starts at a turnout parking area just to the south. The campground office can point you in the right direction.

      The steep, unnamed path from the Mammoth Campground ▸2 joins the Lava Creek Trail (also called the Boiling River Trail) just before the main trail winds around the thermal source that emanates from an off-limits cave, thought to be resurfacing runoff from distant Mammoth Hot Springs. The official Boiling River soaking area, ▸3 indicated by split-rail log fencing, is at the far end of the trail, 0.5 mile from the trailhead.

       To keep the Boiling River family friendly, a couple of rules are strictly enforced: bathing suits are required, and alcohol is prohibited.

      Geothermal

      Signs warn of the possible presence of the pathogenic bacteria Naegleria fowleri, but no cases of the rare meningitis caused by the microscopic amoeba have ever been reported here. Just to be safe, do not submerge your head or nose below the water—the amoeba enters the brain via the nasal passages. Symptoms include a runny nose, a sore throat, a severe headache, and in the worst cases, possible death within a few days.

      Swimming

      Bathing in the near-scalding main thermal channel would be fatal and is prohibited. (See “Bathers Beware”). The actual composition of the dynamic bathing area changes daily and with the seasons. Seek out spots where other soakers are congregating, and beware of direct contact with undiluted thermal water. If you have trouble finding a calm spot where the current does not wash you downstream, try placing a big river stone in your lap.

      Do not overdo the soaking, especially if you have to make the steep alternative hike back up to Mammoth Campground afterward. When finished, retrace your steps to the campground or parking areas. ▸4

       MILESTONES

▸1 0.0 Start at Boiling River/Lava Creek trailhead

▸2 0.4 Junction with trail from Mammoth Campground

▸3 0.5 Boiling River soaking area

▸4 1.0 Return to parking lots