Wildlife, sport and activities, sometimes all at once

(Editor's Note: This story first appeared in the July 2007 issue of Mammoth Monthly magazine. Subscribe here.)

The September 8 High Sierra Fall Century bike ride is like no other.

Viewed from a geological perspective, the hundred miles, beginning and ending at the Whitmore Ballfields just south of Mammoth, the ride is a geology tour de force in which riders travel from the present through the very recent geological past, back in time through the Cambrian Period and back again.

Millions of years pass before the cyclists' eyes, if only they knew how to look at the landscape.

Mammoth geologist Bob Drake recently accompanied a pair of journalists on a tour of the hundred miles, offering his knowledge and perspective on one of North America's most active (still) geological laboratories.

With maps spread out on his lap he told stories of recent and ancient tectonic and volcanic events, each of which are easily viewed from the roads -- U.S. Hwy. 395, Rte. 120 and the Benton Crossing Road -- that the cyclists will ride September 8.

THE START

This isn't a ballfield. In fact, it is the floor of the huge Long Valley Caldera, formed 760,000 years ago in one of the biggest volcanic eruptions ever in North America. The titanic event lasted just forty hours and blew ash all the way to Nebraska and southern Texas. In this unimaginably violent event, the ballfields were at about the height of the Sierra Nevada. In one incredible day, the volcano blew, the earth sank about five miles and, bubbling out from beneath came molten rock that we now recognize as Bishop Tuff -- the reddish-brown rock that is ubiquitous inside and just outside the caldera.

THE FIRST CLIMB

As riders approach the climb to Deadman Summit on 395, they will see on the left the Inyo Craters, still covered with nothing but pumice on the top. These are some of the most recent volcanoes in North America, and form the southern end of a nearly straight line of small volcanoes that stretch from Mammoth Mountain to Mono Lake. The magma that created these craters never reached the surface, thus there is no fresh ash or solidified lava there. These craters were formed when heat from the raising magma superheated groundwater until the overlying dirt and rock could no longer contain the pressure, resulting in a massive steam explosion. Radiocarbon dating of a log buried in the debris blanket gave an age of 650 years.

The climb itself represents the western wall of the old caldera, giving fresh perspective to the riders' term: A wall. This time, it's literal.

DESCENT TO JUNE LAKE JUNCTION

Now the riders are on the back side of the Long Valley Caldera. While continuing to enjoy the eastern escarpment of the Sierra Nevada, they come face-to-face with what looks like a huge slag heap. This is Wilson's Butte, formed over many years when it bubbled and oozed and rose from the surface. About 1,350 years ago. That's just yesterday in geologic time.

On their way to the junction at the bottom of the grade, cyclists can look to their left (if they care to slow down, that is) and see a terrific view from an unusual perspective of Mt. Ritter and Banner Peak, set back from the escarpment but easily visible.

THE MONO LAKE BASIN

At the junction of 395 and Rte. 120, cyclists are at the foot of the Mono Craters, with Panum Crater on the left and the others on the right. Radiocarbon dates for the Mono Craters gives ages of five hundred-fifty years for the youngest dome to forty-thousand years for the oldest. All but four of the twenty four exposed domes and flows of the Mono Craters are less than ten thousand years old. The most recent eruptive episode occurred between 1325 and 1365, during which time there were several explosive eruptions and five separate lava flows that oozed onto the surface.

As Rte. 120 heads south, cyclists will ride through the Mono Craters "coulee," a viscous ryolith flow, and continue through a beautiful, white pumice apron that are dotted with Jeffrey Pines.

SAGEHEN SUMMIT

Here the participants in the bike ride will get their first full-on views of the White Mountains, set against the foreground of the Glass Mountains. The surface here is a pink Bishop Tuff sheet that has filled in, but the contours of the earth make it easy to imagine the flow of rock underneath. This Bishop Tuff is mantling Sierra Nevada granites that occasionally poke their heads through the surface. So riders are really in two mountain ranges at the same time.

The White Mountains are a fault block mountain range that extend for approximately sixty miles, and are approximately ten miles wide. The northern end of the range extends slightly into Nevada, creating that state's highest point, Boundary Peak. The highest point in the range is White Mountain Peak, which at 14,252 feet is the third-highest in California. This peak is the remnant of a volcano rising some four hundred meters above the surface from which it erupted before the range was tectonically uplifted.

And, in fact, back in the Cambrian Period, the Whites used to be the California West Coast before the Sierra Nevada rose. (Back in Mammoth, the iconic "Mammoth Rock" is actually a limestone reef that was pushed up from the ocean floor.)

WILDROSE SUMMIT

Here is a magnificent view of the Sierra's Mt. Tom and the Wheeler Crest, rising above a Bishop Tuff sheet. If there is a more beautiful view from any bike ride anywhere, we'd like to see it.

WATERSON DIVIDE

From this vantage point it is fun to imagine what is underfoot, that is to say, the Glass Mountains. These mountains, formed largely of obsidian, form the wall the eastern wall of the Long Valley Caldera, and were here before the Big One blew. Glass Mountain itself gets its name from the rhyolite and obsidian flows that compose it. These rocks are especially high in silica.

THE FINAL DESCENT

As cyclists zoon back down into the caldera from Waterson Divide and begin the lovely finishing ten miles along the shores of Crowley Lake, they will get terrific views of Glass Mountain from inside the caldera, as well as grand views of Mt. Morrison in the Sierra Nevada.

THE FINISH

No wonder these bike riders are tired! They've gone a hundred miles on their bikes, experienced the remains of a huge volcanic outburst, taken in the sights of recent volcano activity and visited the ancient shore of California, right where they wouldn't expect to see it.

The High Sierra Fall Century isn't so much a bike ride as it is a graduate course in the School of Rock.

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