Isosceles Pass
Peak · 12,099 ft · Eastern Sierra corridor
Isosceles Pass is a 12,099-foot peak in the Eastern Sierra's high alpine corridor, accessible via approach from the Mammoth Lakes region. Wind-exposed and avalanche-terrain-significant.
Wind dominates here. The 30-day average of 12 mph masks afternoon gusts that regularly hit 46 mph, funnelling off the eastern exposure. Cold persists; typical conditions sit around 19 degrees Fahrenheit even in spring. Morning windows close fast; expect exposed ridges to be unworkable after 11 am on windy days.
Over the last 30 days, Isosceles Pass averaged a NoGo Score of 37.0 with wind averaging 12 mph and temperatures holding near 19 degrees Fahrenheit. The rolling pattern shows the 30-day minimum score of 9.0 against a maximum of 65.0, reflecting the pass's volatility. The week ahead will track similar exposure and wind behavior; plan for afternoon deterioration and avalanche-terrain caution in active snowpack zones.
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About Isosceles Pass
Isosceles Pass sits at 12,099 feet in the Eastern Sierra corridor, accessed primarily from Mammoth Lakes via high-country approaches. The pass marks a windward ridgeline on the Sierra crest, with direct exposure to prevailing westerlies. Winter and spring snowpack, combined with consistent ridge wind, makes this an avalanche-terrain location managed by the Eastern Sierra Avalanche Center. Access requires high-clearance or foot travel; Highway 395 is the main regional spine, with Mammoth Lakes serving as the primary gateway town approximately 10 to 12 miles south. The pass sits above treeline and is rarely sheltered.
Conditions at Isosceles Pass follow a high-altitude ridge pattern. The 30-day average wind of 12 mph is misleading; gusts reach 46 mph in the rolling 30-day and 365-day records, and wind funnels strongest in afternoons. Temperature averages 19 degrees Fahrenheit over the last month, with a 365-day range from 5 degrees to 32 degrees Fahrenheit, making this a cold-season destination. Spring brings snowpack and active avalanche conditions; summer offers brief windows of stability but crowds remain light (2.0 average crowding on the rolling 30-day metric). The pass sees its lowest NoGo Scores (minimum 9.0 in the last 30 days) on rare calm mornings, typically in early season transitions.
Isosceles Pass suits experienced mountaineers and ski tourers with avalanche training and winter mountaineering skills. The pass is not a casual day hike; it demands avalanche awareness, rope work for winter approach, and comfort on exposed ridges. Visitors plan around snowpack stability, wind direction, and time-of-day wind patterns. Parking at Mammoth Lakes trailheads fills quickly during holiday weekends and early spring when the route becomes passable. The base popularity metric (0.2) reflects low overall visitation; most visitors are specialists or locals with prior experience on Eastern Sierra alpine terrain.
Nearby alternatives include Mount Ritter and Banner Peak to the south, which sit in the same avalanche zone and wind corridor, and the Mammoth Crest to the west, which offers similar high-alpine exposure but slightly lower elevation. Visitors pairing Isosceles Pass with a multi-day alpine traverse should account for the Eastern Sierra's rapid weather shifts and the consistent afternoon wind. The pass's low crowding makes it attractive for solitude-seeking mountaineers, but the trade-off is exposure; there is no shelter, no water, and limited objective safety in poor conditions. Plan trips around the rolling calm windows, typically early morning or periods when the rolling 30-day score dips below 30.