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Mount Tehama:
Brokeoff Mountain & Mount Diller

Mount Tehama

If you had visited this area a few thousand years ago, Mount Tehama would have risen to 11,000 or so feet before you, stretching from what is now Mount Diller to Brokeoff Mountain.

There are at least three theories about what happened to Mount Tehama.

  • According to the Lassen Volcanic National Park brochure, what happened to Mount Mazama in Oregon also happened to Mount Tehama. After growing for hundreds of years, Mount Tehama erupted and collapsed. The difference is that Mount Tehama's caldera developed an outlet, so the rain and snowmelt run out instead of filling up the caldera.

  • Jeffrey P. Schaffer, in Lassen Volcanic National Park & Vicinity, says Tehama was eroded away by glaciers, as was Mount Maidu, which predated Mount Tehama by many, many years.

  • Stephen L. Harris, in Fire Mountains of the West, says Mount Maidu grew, blew, and collapsed. Many years later Mount Tehama, or Brokeoff Volcano, as he calls it, grew and was mostly eroded away, leaving Brokeoff Mountain and Mount Diller as remains. Lassen Peak eventually grew on the flank of the former Brokeoff Volcano.

One of these versions, or perhaps a combination of the three, is probably essentially correct.

At any rate, what is left of Mount Tehama is mostly in Lassen Volcanic National Park, close beside Lassen Peak. Though less well-known than its volcanic plug neighbor, Mount Tehama is a significant mountain in its own right. Its two most prominent projections are Brokeoff Mountain and Mount Diller, shown here from two different directions and distances. In both photos, Brokeoff Mountain is to the left, Mount Diller to the right.

Brokeoff Mountain and Mount DillerBrokeoff Mountain and Mount Diller

Brokeoff Mountain in the fall

Brokeoff Mountain in the fall.

Sulphur Works

Sulphur Works, an active volcanic area reminiscent of Yellowstone, is directly under the presumed crater of Mount Tehama.

Now, would you like to learn more about the volcanic area at the southern end of the Cascades? Yes? Read on.

As you are driving along I-5 in the Red Bluff/Redding area, if you look to the east you will, weather permitting, see something similar to this (with varying degrees of snow cover by season):

East of I-5 in Red Bluff/Redding area

"Just look how big that mountain used to be!" you exclaim. True, it was big. And the scene over there certainly looks as though a huge mountain stretched clear from present-day Lassen Peak to Brokeoff Mountain. But no. It wasn't so.


Too bad. This (below) is more what Mount Tehama really looked like. Still a big mountain, but not nearly as big as you had thought. In volcanology, as in almost everything else, looks can be deceiving.

That's more like it

©D.L. Mark 1997

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