Crater east of Shasta? Geologists, please read.

Last time I flew up to Washington I saw something that I thought might be an impact crater. We were at about 30,000 feet and Mt. Shasta was off of the left wing. There was a large, circular depression in the ground with a “berm” around the north or north-eastern edge. It had been filled in by who-knows-how-many years of natural processes. I don’t know how far east it was from Shasta, but I’ll guess about 50 miles. I saw a similar, less well-preserved structure miles north of the first crater. I’m not sure of the diameters, but they were about one inch as seen from our altitude.

California is at the edge of the North American tectonic plate, and the Pacific plate is near the coast that far north. Shasta is a dormant volcano. Could these structures have been the remnants of very small volcanos? Or are they impact craters from meteorites?

Unfortunately I don’t have the coordinates. I’ll have to carry a sectional with me next time.

Kinda sounds like the tops of a volcano from what your talking about. It’s been a long time since I’ve even studied any physical Geography though.

What sectional does it fall on and what airport is close and I can look it up, that is if you are talking about a flight sectional, they’re all in a cabinet about 10 feet from me.

50 miles east of Shasta is Lassen Nat’l. Park – Home to Mt. Lassen, the Lower-48’s premiere volcano until that damn upstart Mt’ St. Helens, decide to get into the act. In may 1915 Mt. Lassen blew its top big time.

Were you possibly confused with Mt. Lassen and Brokeoff mountain from Lassen National Park???

Ha, ha. Beatcha by a hair, China Guy!


The area is on the Klammath (south) sectional, but I looked on mine and didn’t see it. The crater was pretty-much at ground level, so that’s probably why it’s not on the chart. I was thinking that if I had a sectional in the airplane, then I could figure out its approximate position. The reason I asked about an impact crater is that it was not on a mountain, but in a plane. What I’d really need to look at is a contour map of the area east of Mt. Shasta.

Just eyeballing the sectional, and not being in an airliner for verification, I’d say it’s somewhere south of 30ºN, 122ºW. But 1:500,000 isn’t good enough resolution to show it.

Possible. I had been asleep shortly before I looked out of the window (it’s so easy to fall asleep when you aren’t at the controls), and when dad and I would fly north we would be on the west side of Shasta at about 10,000 feet, and not east and three times higher. But Shasta is about the biggest thing in the area, so I’m pretty sure that was it.

Now that I think of it, I’m not entirely sure the crater wasn’t northeast of the snowy mountain. But I’m pretty sure that it was, if not directly east, then mostly east.

There’s nothing shown near Shasta in this map of north american impact craters. The craters you saw were probably a volcanic grouping.

Dang, Styguy, simulpost. You’re not from around them parts are ya? I went to Lassen at least 20 times over 20 years. It was the first “peak” I ever climbed.

well no wonder I couldn’t find it, I’ve got Mt Shasta at Lat: 41.3225 Lon: -122.314716 from Map Blast and not 30 N. I might be able to find some better maps around here of the area.

Now that you say something though about it being level I’m wondering if it’s an old lake.

Lassen is more to the southeast of Shasta, and a bit more than 50 miles away. Also, Lassen erupted by dome collapse, and there is no large circular volcanic depression there.

A better candidate, which:

  1. is ~50 miles east (and slightly north) of Shasta; and
  2. is a caldera volcano, which are characterized by large, circular depressions, is

Medicine Lake Volcano, which erupted ca. 50 BC, ca. 720 AD, ca. 800, ca. 825, ca. 885, and ca. 1075, and possibly in 1910. (Volcanoes of the World, second edition).

If Mount Shasta was on your left and you were looking at something a few tens of miles away, could it be you were looking at the Medicine Lake caldera in Lava Beds National Monument?

map of Mount Shasta in relation to Medicine Lake

more info on Medicine Lake

The Medicine Lake caldera is part of a shield volcano, which by definition has a low, flatish profile that might look ground-level from a distance.

I unfortunately can’t seem to get everything in one frame to post a link… but if you go to, type in “Medicine Lake, CA” as a location, and then size the map to 1:200,000 scale and “large,” you might see enough of the terrain to doublecheck your location.

On preview, I see Pantellerite has beaten me too it. :slight_smile:

For god’s sake, someone page Geobabe. We were just joking about the dearth of geology threads.

Anything look familiar?

And an overview map of potential candidates in the Cascades:

Well, Fillet, you did beat me to the links at least!

I’ve flown over that area many times. There are tons of ancient volcano cones between Shasta and Bend, all over the damn place. I’m betting on a caldera.

In addition to the other fine links, and though it isn’t what you saw, see also Crater Lake National Park for an additional volcanic formation in the general area.

I was rushing through the map in dim light. I thought 30º sounded a bit low, but I was in a hurry to get into the shower.

Didn’t see anything that looked familiar in the photos. I’m going through the topo link fillet provided. It crashed my browser once, so I’m trying again.

The only thing that would lead me to believe is is a strike is that it’s flush with the ground. When I think of calderas I think of craters on top of mountains. But I’m not a geologist, so that may just be my layman’s thinking. Two things that came to my mind as we flew over the area last summer, was that A) the area is volcanic; and B) you’d think that The Discovery Channel would have mentioned strikes in the Siskiyous in one of their meteorite programs. So you’re probably right that it is a caldera.

When dad and I would fly out to Las Vegas (“for lunch”, but it was really just to have someplace to fly to) I would look at the desert passing below. There were rocky outcroppings surrounded by sand. (I never found out if the sand was from the rocks, or if it had been covering the hundreds-of-feet high rocks and were slowly revealing them.) You could see where the water would flow in the rainy season. You could see the colours of different strata. That always made me regret not taking Geology classes.

Well, I’m a geologist, from the bay area, but since I went to school in MI, I’m not completely familiar with all of CA. And, I’m an environmental geologist, (meaning I help clean up pollution), so this might be a little out of my area. (man, what a hedge) But from what I’ve read, you probably saw a caldera. Not all of them are at 11,000 feet.

Actually, it’s both. As those rocky outcroppings were thrust up, erosion accelerated. So that sand is probably quite deep, and has come off the rocks, along with some that was blown there by the wind. Eventually, it will even out. It’ll just take a loooooong time, depending on rainfall, hardness of the rock, its chemical reactivity, and rate of upthrust.

After posting, I reread that last paragraph, and I’m not real happy about it. The sand is eroding off of the rocks, so it isn’t revealing them so much as burying them. Until some cataclysmic flood comes and washes it all away- which might have happened on Mars- I’m not sure if the final interpretattion of the data has been made. Better example- Yosemite valley would be much more spectacular if the erosional deposits were not there. There is over 1000 feet of sediment that has washed off the surrounding mountains. Sometime down the road a bit, the mountains will be ground down, and the valley will be filled, and it will be a lot easier to climb El Capitan.

Rocks that are exposed by erosion usually are at the tops of hills with shallower slopes than the ones I think you are talking about out in the desert.

You rang? Now if only someone would ask a question I actually know the answer to…