Crowley Lake Columns

A reservoir and an old eruption

Crowley Lake is a reservoir on the upper Owens River in southern Mono County. The Los Angeles Department of Water and Power created it in 1941 by building Long Valley Dam, as storage for the Los Angeles Aqueduct and for flood control. It is named for Father John J. Crowley, the “desert Padre” of Owens Valley history. Mono County’s visitor bureau notes that the basin was meadowland before the dam went in.

The rock along the east shore is far older. About 760,000 years ago a very large eruption formed the Long Valley Caldera and released hot ash that cooled into the Bishop Tuff, which is common across the area. After the reservoir filled, wave action cut into the tuff along the eastern shoreline and exposed rows of columns that nobody had described before.

How the columns formed

For decades the columns had no detailed study. A UC Berkeley team led by Noah Randolph-Flagg worked on them, and in 2017 the group published “Evenly spaced columns in the Bishop Tuff (California, USA) as relicts of hydrothermal cooling” in the journal Geology. The paper’s abstract says the columns resist erosion better than the surrounding tuff because of mordenite, a zeolite that forms at low temperature (100 to 130 °C). The authors propose that the columns formed when cold water seeped into the still-cooling tuff and became unstable where liquid water met steam. Wikipedia sums up the same work: snowmelt soaked down into the hot ash and rose again as steam, and the minerals it left behind outlasted the ash that eroded around them. The paper says the formation process needed fairly gentle ground, and that columns like these are a rare look at hydrothermal processes that may be widespread.

What is there

The researchers counted nearly 5,000 columns spread over a few square kilometers. Wikipedia gives the area as 4,000 acres. Reported heights vary. Wikipedia and Geology In say some columns reach about 20 feet. The American Southwest guide puts the largest at about 15 feet and the cliffs at “up to 15 feet or so.” Some columns stand upright about a foot apart and are capped by arches. Others lean, or lie half buried and look like vertebrae. The biggest and most widely spaced columns line the north side of a small bay. South of it are higher cliffs with caves, arches and orange-brown coloring.

Visiting

The approach starts on Owens Gorge Road at Toms Place, crosses the top of Long Valley Dam, and then follows unpaved tracks. The American Southwest guide describes a 2WD trailhead a short way past the end of the pavement. From there it is about 1.9 miles on foot, or a drive that needs 4WD for one rough, steep spot. Showcaves.com warns that recent rain can make the track impassable and lists entry as free as of 2020. Geology In notes there are no facilities and little shade. Snow affects the road in winter. Visit Mammoth strongly discourages the land route. It says the steep, unmaintained trails are prone to landslides and cross restricted property managed by LADWP, and it recommends viewing the columns by launching a non-motorized craft or boat from Crowley Lake Fish Camp. If you plan to go overland, first confirm that the route is open and that you are allowed to use it.

Lake level matters. When the reservoir is high, most of the formations are underwater or cut off, so check the level before making the trip. The columns are fragile even though they look solid. Geology In reports that geologists ask visitors not to climb on them or break them. The American Southwest guide lists management as Mono County, and the reservoir itself is part of the LADWP aqueduct system. Follow any posted rules.