The high concentration of soil CO2 is a result of magma shifting deep beneath the Mammoth Mountain volcanic complex.
Trees in the area died because their root systems were suffocated by CO2, which displaces oxygen in the soil.
Horseshoe Lake is known for having a naturally sandy beach, which is a relative rarity among the other surrounding granite-rimmed lakes.
The CO2 levels are monitored by the U.S. Geological Survey (USGS) to track the volcanic activity of Mammoth Mountain.
The lake level fluctuates significantly based on annual winter snowpack and seasonal snowmelt cycles.
Horseshoe Lake is a high-altitude alpine lake located in the Mammoth Lakes Basin, notable for its volcanic geological activity. The area is defined by a significant stand of dead trees caused by high concentrations of carbon dioxide seeping from the volcanic soil below. The loop trail is a relatively flat, 1.8-mile path that encircles the water, providing consistent views of the Mammoth Crest and Crystal Crag. It serves as a primary access point for the Lakes Basin Path, connecting various lakes and hiking routes within the Inyo National Forest. Due to the volcanic emissions, certain low-lying areas near the lake are restricted to prevent CO2 exposure. The site remains a primary destination for dog owners and hikers due to its accessible terrain and scenic proximity to Mammoth Mountain.
The shoreline looking south toward the jagged granite peaks of Crystal Crag.
Stay on the clearly marked trails, especially in the designated tree-kill zones, to avoid potential CO2 accumulation in low-lying depressions.
Bring extra layers as the elevation is above 8,900 feet and temperatures can drop rapidly even in mid-summer.
The trailhead is a popular starting point for longer hikes; confirm your route plan before departing as cellular service is intermittent.
Do not enter fenced-off or signed low-lying areas, as these are identified hotspots for hazardous gas concentration.
Access is restricted during winter months due to heavy snowfall and road closures; generally accessible by vehicle from late spring through late autumn.
Keep dogs on a leash and stay strictly on the trail to avoid carbon dioxide hazards in low-lying areas.
