What Really Happens On a Hike into Amboy Crater?

On a cool fall morning, I traveled to the Mojave Trails National Monument and joined a geology-focused hike of Amboy Crater, one of Southern California's most well-preserved volcanic cinder cones.

Amboy Crater was designated a National Natural Landmark in 1973 and is among the most frequented spots in Mojave Trails National Monument. It provides a rare chance to delve into Earth's volcanic past and explore one of the youngest volcanic fields in the United States.

Amboy Crate rises 250 feet above the floor of a vast valley. Its dark blackish color sits in sharp contrast with the earthy tones of the surrounding desert when viewed in Goggle Maps.

As far as "fire mountains" go, cinder cones are the most common type of volcano in the world and aren't terribly big but they certainly embody the classic form of a stereotypical volcano: conical, steep-sided and usually topped with a crater. They may be anywhere from dozens to hundreds of feet high, but they rarely exceed 1,200 feet. Standing 250 feet above the valley floor, Amboy perfectly fits this prototypical description of a cinder cone.

Trail to the Crater

A well-defined 1.2-mile trail winds its way through a lava field that extends from the parking area to the crater's base.

The lava field, mainly composed of pahoehoe lava, covers an area of over 27 square miles. Pahoehoe lava results from eruptions that gradually releases low viscosity lava onto the surface and results in a smooth, ropy, and billowy texture. The geologist leading the hike pointed out this section of the lava field, which highlights the ropy characteristics of pahoehoe lava.

How do Cinder Cone Volcanoes Form

Cinder cones tend to develop very quickly and form when lava erupts as relatively benign liquid fountains. During the eruptions, small lava fragments are spewed in the air and solidify instantly into porous rock known as cinders. If an eruption of this type continues long enough, cinders accumulate to form the the unique cone-shaped structure shown in this photo.

Lava rarely flows from the top of a cinder. Instead, lava typically rushes out from a breach in the side walls or a vent near the base. This is because cinder cones can not support the pressure exerted by a violent volcanic eruption.

Layers of Ash and Cinders

As we approached the base of the volcano, the lava field became littered with various sized cinders.

On the trail looking up at the cone formation.

A 0.4 mile path to the rim heads around the cone's western half and leads to a breach on the west side of the crater.

Looking back at the switchbacks leading to the inner crater and rim trails.

From this vantage point, we could see the vastness of the lava field on the volcano's west side. Most sources estimate the field to be 7-15 feet thick. The light brown areas consist of wind-blown sand trapped in the lava cracks and crevasses.

It’s decision time when you reach the breach in the side wall.

The Inner Crater Experience

Our group decided to first hike into the crater and then walk along the rim.

A gentle sloping path leads to the floor of the crater. Amboy has had at least four distinct periods of lava eruptions with the most recent eruption occurring about 10,000 years ago.

The eruptions are considered as having been of relatively low force, with most experts suggesting they were not major explosive events, but rather moderate to low intensity lava flows.

As we walked on the crater floor, it was clear that Amboy consists of not just one cone, but at least four cones nestled within the primary crater. The additional cones are delineated by windblown sand and small walls, which we crossed on our way to the east rim.

On the Rim

The expansive view from the east wall highlighted the numerous cones and the significant breach in the west wall. It’s believed an explosive event resulted in the destruction of this large wedge of the cinder cone wall.

Amboy like most cinder cones, ended its life with an outpouring of black basalt lava that flowed across the landscape.

Even though the rim appears narrow from afar, there is ample room to walk safely.

A group of hikers walking along the rim trail provide perspective highlighting the immensity of Amboy Crater.

Returning to the Desert Floor

After exploring the crater for 3 hours, we began our descent to the desert floor.

Today's adventure was a great introduction to volcanism in the Eastern Mojave Desert. Hopefully our travels will bring us back to the Mojave so we can explore the nearby Cima volcanic field.