Gold under massive ancient lava flows

Of all the ancient gravel channels in the gold country that proved so productive two, one in the north and the other in the south, could well have been the richest and the most difficult to mine of any because they were buried under ancient lava flows hundreds of feet deep. The Tuolumne Table Mountain extends across the county like a gigantic black wall, with basalt sides nearly perpendicular and a bare flat top. It was formed 9 million years ago by and a now extinct volcano. The Little Walker Caldera is all that remains of this volcano and can still be seen east of the Sonora Pass. One of the most impressive geological formations in Tuolumne County, the lava flow runs southwest along the modern Stanislaus River from the pass to Knight’s Ferry with a width of up to a quarter mile and rises over a thousand feet in places.

Tuolumne Table Mountain

After the lava cooled and hardened the softer earth around it slowly eroded over millions of years leaving not only the hard basalt exposed, but in some places, especially along the northern side, the ancient gravel bed lay exposed as well. And it was from this side that most of the many tunnels that were dug into the rich gold lodes below were started. Any shaft from the top of the mountain had to penetrate 140 feet of basalt, another hundred feet of volcanic sand, fifty feet of mixed sand and clay and finally the twenty-five feet of the ancient gravel channel where the gold would be found at it’s base. Hundreds of millions of dollars in gold was removed from under the lava flow through the years.

Lava Wall on Butte Table Mountain

The Butte Table Mountain starts near Lassen Peak and runs south to the north bank of the Feather River opposite Oroville where there are two distinct ridges, North and South Table Mountain. In the far north the lava flow is covered by other formations but in Butte County the original lava flow was bigger than in the south and had several branches. And, like in the Southern mines, the soft earth eventually eroded away exposing the gravel bed into which the tunnels were dug. In the town of Cherokee the basalt had been denuded from the flow for some four miles allowing easier access to the gold bearing gravel. Sebastapol in Morris Ravine and nearby Oregon City were two other mining sites that benefited from the wealth in this ancient gravel channel.



  1. So much of finding gold and succeeding at gold mining involves (and involved) understanding the geology. When people didn’t and don’t understand it, they discovered gold through pure dumb luck. They panned a stream in exactly the right place, or their burro stopped to stare at something shiny, or — you get the idea.

    Your blog is so interesting, John, I keep coming back!


    • Gold got to different places in different ways. In California it was a combination of volcanic and tectonic actions. In Nevada gold and silver came up in hot water springs, but Montana looks like it has lode gold like California’s Mother Lode. If what I hear is true, just like here, there is a lot more gold yet to be mined up there in Big Sky Country. I dug up a blog about Montana’s gold. Maybe you’d like to see it:

      He says there are still undiscovered lodes in Alder Gulch as well as in Confederate Gulch. How do you find a gold deposit that’s buried underground?

      There’s always a lot of luck involved with gold, especially at the beginning, but miners are smart. A sandbar along the Feather River that looked a lot like a productive bar on the American River was likely to have gold in it too, and more often than not it did.

      Thanks for reading and many thanks for responding. I really appreciate it.

  2. I stumbled on this by accident–sorta like the burro–and will be back again in the future. Always appreciate your writing and will be looking for your book as well.

    Keep at it.

    • Great to hear from you Persia. This is one of my favorite articles. It clearly shows the intimate relationship between California’s gold and it’s history of seismic activity. Thanks for writing.

  3. Mike Tower says

    Thanks John. This is something I did not know and on a subject I’ve always had a keen interest in. You made my day.

    • Glad to help, Mike. They say 80% of the gold in California is still in the ground. I expect they may be right. The power of nature is awesome.

  4. Fascinating. In the 1894 geological survey R.H. Penrose, geologist and brother to millionaire Spencer Penrose (the whole family is fascinating) was one of the only ones to say the Cripple Creek find would go on for some time. Others said that this was a fluke and the gold would run out quickly. Guess he was right for as you know they are still mining the area.

    • I wonder how anybody can tell how long the gold will last. Imagine following a seam of gold in quartz rock. Suddenly it ends. Does that mean there is no more gold? Who knows. Another even more lucrative seam could be less than a foot away in any direction at any spot in the shaft and who is can tell. More power to Spencer Penrose. He knew more than I ever will.

  5. Especially since he was looking at gold in granite, not quartz. If you ever have time read up on the Penrose family. Spencer initially made is fortune in copper in Utah. One brother was a senator that I remember and of course the ‘black sheep’ Spencer (Spec to his friends) and R. H. Colorado Springs is still a beneficiary of his wealth and legacy through the Cheyenne Mtn. Zoo, The Broadmoor Hotel, and of course the El Pomar Foundation along with the Pikes Peak Highway and the Pikes Peak Hill Climb. (I covered a few. Smile)

    • You mentioned Spencer Penrose before but I didn’t know the gold in Colorado was in the granite. I guess the gold doesn’t care. It mixes with whatever is around when its molten and under pressure. The Penrose family do seem to be doing well. A little knowledge of gold goes a long way.

  6. I am looking at a lava flow that has quartz veins running through it. Very small veins.
    It sounds like any gold there would have been pushed along with the active flow rather than mixed in the flow. Would the best place to look be under the lava.
    This bed is in Central America.

    • Joe, gold veins in California were often associated with tectonic activity of the earth’s plates coming together, but as you have seen in this post there were several instances of gold underneath the lava flows. Unfortunately Mother Nature is not that predictable. My sense is that gold in quartz veins was forced there after the quartz was in place but again, things could be different where you are. Good luck to you.

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