Third-Fourth Divide
Peak · 11,977 ft · Mammoth Lakes corridor
Third-Fourth Divide is an 11,977-foot Sierra peak in the Mammoth Lakes corridor, exposed to westerly wind funnel off the lakes below. A serious alpine objective with avalanche terrain and sparse protection.
Wind dominates here. The 30-day average of 13 mph masks afternoon gusts that spike above 30 mph by mid-day. Morning calm windows close by 10 a.m. Exposure is total; there is no shelter once you leave the ridgeline approach. Cold persists even in spring, with 18-degree average temperatures.
Over the last 30 days, Third-Fourth Divide averaged 13 mph wind and 18 degrees Fahrenheit, with gusts topping out near 39 mph. The rolling average score of 37 reflects marginal conditions most days. The week ahead shows typical late-spring variability; plan for afternoon wind shutdowns and monitor avalanche forecasts from ESAC if snow remains.
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About Third-Fourth Divide
Third-Fourth Divide sits at the boundary between Red Cones and Inyo domes on the high Sierra spine east of Mammoth Lakes proper. The peak sits roughly 15 miles southeast of the town of Mammoth Lakes and is accessed via Highway 203 to Mammoth Lakes, then south via Mammoth Lakes Road toward Lake Mary and George Lake trailheads. The approach crosses high-altitude meadows and climbs into mixed talus and scree; the divide itself is a windblown ridgeline exposed to the westerly jet. Base popularity is low (0.2), meaning few people summit on any given day. The peak sees moderate foot traffic only during stable, calm windows in midsummer.
Third-Fourth Divide lives in a cold pocket of the high Sierra. The rolling 365-day data shows minimum temperatures near 4 degrees and highs around 31 degrees, with the 30-day average sitting at 18 degrees. Wind is relentless. The 30-day average wind of 13 mph is deceptive; maximum gusts hit 39 mph regularly. Mornings from dawn to mid-morning are the only reliable calm window; by noon, thermal and orographic wind climb sharply. Crowding averages just 2.0 on the rolling 30-day window, so solitude is nearly guaranteed. Avalanche terrain is present on the north and east faces; late spring and early summer snowpack can be unstable, especially on slopes facing south and west that experience heavy freeze-thaw cycling.
Third-Fourth Divide suits experienced Sierra scramblers and peakbaggers who can move fast in variable wind and cold. The summit is not a leisure hike; the approach requires boulder hopping and micro-route finding in exposed terrain. Weather windows are tight and unpredictable; come prepared to retreat if wind or whiteout conditions develop. Late-spring ascents demand avalanche awareness and a hard-packed snowpack; wet-snow slides are common if temperatures climb above 30 degrees during the day. Head out at first light and plan to be off the divide by early afternoon. Parking at nearby lake trailheads fills on warm weekends but rarely on weekdays.
Nearby peaks in the Mammoth corridor, including Mammoth Mountain proper and the Red Cones cluster, experience similar wind funneling and cold. The divide is quieter than these higher-traffic summits and more exposed than sheltered lake-basin objectives like Arrowhead Lake. Visitors planning multiple Mammoth peaks should sequence Third-Fourth Divide early in a multi-day trip; its morning windows align better with multi-summit push ethics than afternoon options. ESAC avalanche forecasts apply directly; check the Eastern Sierra Avalanche Center's bulletin before any late-spring or early-summer attempt.