Panum Crater at Mono Lake
Photo © Terry Wright
Mono Lake, the Sierra Nevada mountain range, Mono Craters and associated features are all visible from the Panum Crater. A rough trail on pumice (read: squishy footing) leads to the rim and 0.2 miles of further hiking takes you to the spectacular obsidian core of the volcano which erupted 600 years ago.
Directions: From Lee Vining, drive south on 395, take highway 120 east for about 2.5 miles. Look for a small wooden sign which reads Panum Crater next to a dirt road and turn left (north). If you reach the turn-off to the South Tufa Area, you have gone too far. Follow the dirt road for a mile or to the obvious parking area at the base of the crater. From the parking area, you will see two wooden posts with interpretative information. (Lat:37.55.548'Lon:-119.02.784). The Panum Crater is within the Mono Basin National Forest Scenic Area and collection of any rocks, obsidian, or plants is strictly prohibited.
The trail starts here and continues to the top of the crater rim, then down into the crater and switches back up to the crags of the inner dome.
360 degree views start to the north (figure 1), across Mono Lake to Paoha island, an uplift of lake sediments with volcanic core on the east end. Continuing beyond you see Negit Island, a volcanic neck, and on the north shore the broad layered expanse of Black butte, a cinder cone that erupted underwater.
To the northwest lies Lee Vining and the Mono Basin National Forest Scenic Area Visitor Center, a must stop for great displays on the natural and human history of the region. The straight line of range front and lake shore is defined as the fault scarp of the Sierra Nevada fault zone; with recent earthquake activity. On the right skyline, Conway Summit serves as the conduit for Route 395. At a roadside pullover, you can look back on this vista and see Sierra Nevada granite overlain by glacial moraines across the road. (figure 2) The crisp, straight mountain front is defined by the Sierra Nevada Fault Zone, where the high plain of the Sierra Nevada broke off 10 million years ago and the area of Mono Lake sank to a broad basin. This same event occurred along the entire eastern Sierra Nevada front. The Basin and Range to the east is actively pulling apart to form individual mountain ranges, from the air looking like a herd of caterpillars crawling north out of Mexico.
In the west view, the long low ridges that emanate from u-shaped canyons are glacial moraines. U-shaped canyons were scoured in bedrock by glaciers as recently as 10,000 years ago. Grey cliffs of granite alternate with reddish layered cliffs of metamorphosed sediments. These are roof pendants; remnants of oceanic layers intruded and baked by molten granite magma. Directly west, looking carefully you can see Blood canyon, with two moraines, one older to the left and a younger one cutting it to the right (figure 3). The relative age of the moraines is shown by the sharper, younger moraine on the right cutting the more subdued older moraine on the left.
The southwest vista is a gaggle of sharp mountains, rising above the June Lake basin, with ski areas June Mountain and Mammoth (figure 4). The range of knobby peaks to the south are the Mono Craters, erupted from deep magma along a straight fault line (figure 5). The source of magma is the leftovers from a body that now exists 3 km under Crowley Lake to the south out of sight over Deadman Summit. Crowley was the site of a huge volcano which exploded 750,000 years ago filling the air with dust and ash. A foot of ash accumulated in North Dakota, and a wave of incandescent glass ash and gas swept out to the north, south and east. This deposit is called the Bishop Tuff, which today stands as pink holey cliffs along 395 towards June Lake and Bishop.
To the west of the Mono Craters, east of 395, you can see a low mountain which is grey granite, and on the ridges to the north of this are two trails of pink Bishop tuff (figure 6). These are the tails of a bow wave of Bishop tuff that was split around the mountain as the wave traveled north. Western part is called "aeolean buttes" so called because they look windblown, really a misnomer because they were formed of volcanic tuff. Bishop tuff covered the entire Mono Basin and has been encountered in drill holes on Paoha island inter-layered with lake sediments, an indication that Mono Lake is at least 750,000 years old.
To the east, low hills and valleys form on older volcanic rocks, overlying granite. The broad basin below is the ancient bed of Mono Lake, which used to drain to the southeast through Adobe Valley. Bristlecone pines live in the harsh environment on ridges. This area is accessible by 4 wheel drive vehicle through Adobe Valley if you continue east on 120.The forested ridges were the site of Mono City, a lumber town where a railroad carried lumber to the Bodie mining camp high on the mountains to the northeast. This is now a state park replete with mining memories.
Panum Crater itself is a Plug Dome, a two stage volcano with an outer pumice rim and an inner jagged core of obsidian layered with pumice. The rim erupted first from a fountain of pumice formed as gas charged magma expanded as it met the water table and shot out of the ground. The plains around and the rim formed at this time. At one point an explosion occurred and an avalanche of volcanic blocks blew through the rim, forming a notch to the north. This is a classic coulee, generically a gap in anything, here formed by a volcanic avalanche (Figure 7).
After some time, the magma eruption lost momentum and a sticky mass, like toothpaste, emitted from the crater. We see this as the obsidian core with jagged outcrops and knife sharp fragments. A hike up here is rewarded by spectacular outcrops of streaked pumice and obsidian. As the mass erupted it folded over onto itself and formed pinch and swell "boudinage" structures. The best place to see these is to the right of the zig-zag trail that leads to the summit. At a small tree on the right, follow a rough trail to the floor of the crater. Folds and boudinage in streaks of pumice and obsidian adorn the black slabs at the base of cliffs (Figure 8).
Blocks scattered around and cliffs are the remnant of the last eruptions of thick viscous lava. This extruded as a series of spires, which collapsed under their own weight, forming the unstable rough topography we see today.
Panum Crater is a wonderland of rock and vista, to be enjoyed carefully by all. Please do not collect any obsidian or rocks from this protected area.
Hiking and photography.
Fees: Guided groups must apply and pay for a permit. Inquire at the National Forest Visitor Center in Lee Vining.
Not accessible to wheelchairs due to unstable pumice soil.
National forest rules apply. Dogs must be on a leash and owner control only.