Panum Crater

The dome as seen from where the trail tops out on the tephra ring. slgwv (Atlas Obscura User)

Looking toward the high point of the tephra ring on the southeast side. slgwv (Atlas Obscura User)

The dome and the tephra ring, with Mono Lake in the background. slgwv (Atlas Obscura User)

View of the central part of the dome, from the trail. slgwv (Atlas Obscura User)

Looking north toward Mono Lake through the middle of the dome. slgwv (Atlas Obscura User)

One of the dome summits. slgwv (Atlas Obscura User)

View west from the dome trail toward the Sierra Nevada. The main access trail is in the foreground. slgwv (Atlas Obscura User)

Looking north to Mono Lake. West part of the tephra ring on the left; dome on the right. slgwv (Atlas Obscura User)

Edge of the dome (to right) and western part of the tephra ring. Mono Lake in the distance. slgwv (Atlas Obscura User)

Block of dark obsidian. Foot for scale. slgwv (Atlas Obscura User)

Ragged lava toward the middle of the dome. Some obsidian is visible. slgwv (Atlas Obscura User)

Panum crater at dusk Avoiding Regret (Creative Commons)

Hiking Panum Crater at dusk Avoiding Regret (Creative Commons)

Looking east off the tephra ring to an older dome, Dome 5. Note it lacks a tephra ring. slgwv (Atlas Obscura User)

Looking south along the dome. Older Mono-Inyo domes are skylined at left; Sierra Nevada skylined at right. slgwv (Atlas Obscura User)

Rhyolite away from the dome edge. Little obsidian is present here because the rock cooled more slowly. slgwv (Atlas Obscura User)

Looking northeast toward Mono Lake from the south part of the tephra ring. slgwv (Atlas Obscura User)

Looking north to Mono Lake. Tephra ring at left; dome at right. Near where the trail tops out coming from the parking lot. slgwv (Atlas Obscura User)

Obsidian-rich rock off the dome trail. slgwv (Atlas Obscura User)

View of Panum Crater down the access road, showing both the tephra ring and the ragged central dome. slgwv (Atlas Obscura User)

Interpretive sign at the trailhead. slgwv (Atlas Obscura User)

Looking east along the tephra ring (to right). slgwv (Atlas Obscura User)

Obsidian pinnacles. slgwv (Atlas Obscura User)

Upthrust pinnacle of obsidian. slgwv (Atlas Obscura User)

Blocky obsidian off the dome trail near the edge. slgwv (Atlas Obscura User)

Upthrust obsidian off the dome trail. slgwv (Atlas Obscura User)

Dark obsidian in place. slgwv (Atlas Obscura User)

(Left to right) The dome, the tephra ring, and Mono Lake, on the east side. slgwv (Atlas Obscura User)

Looking across the dome to a summit on the east side. slgwv (Atlas Obscura User)

Panum Crater, just south of Mono Lake, is the youngest and northernmost of the Inyo-Mono Domes (or Craters). These are a distinctive set of small domelike volcanoes nearly all consisting of rhyolite, lava with a high silica (silicon dioxide) content. Molten rhyolite has a consistency like toothpaste, and because of this high viscosity, it tends to form glass when it’s cooled quickly. Nearly all obsidians have a rhyolite composition.

The eruption starts with a fountain of ash (“tephra,”) of which some falls out in a ring around the vent while the rest is dispersed. Later rhyolite magma is extruded. Since it’s so viscous, it doesn’t flow far but builds up in the center of the vent to form a dome. The rhyolite also typically forms massive obsidian around the edges because it cools more quickly there. This can be seen at the dome in Panum Crater.

Uniquely, Panum Crater is so geologically young that the tephra ring is preserved. Being just loose material, it erodes away geologically quickly, and no rings are left around the older domes.

Know Before You Go

Go about three miles east of US-395 on CA State Route 120. The crater will be obvious on the north (left). Turn left at the signed turnoff and proceed a little less than a mile on a graded road.

The road tends to be rough but should be passable with care to ordinary passenger cars in dry weather. The road goes to a trailhead with an interpretive kiosk. The trail heads to the crest of the tephra ring, from which trails can be taken either way around the ring. A branch trail also heads to the dome itself, and you can climb up into it. Please stay on established trails in the loose material.