When was Arizona underwater?

Factual Questions
1

Arizona has some amazing geology. It’s full of beautiful rock stack with horizontal stripes like this.

As far I understand, this was all once sea bed. The oceans deposited layer upon layer of sediment. The composition of sediment changed over time. This accounts for layers o0f different colour. The oceans receded. The sediment changed to rock. And then erosion wore most of the rock away, leaving a few stacks.

Is that correct? Please fight my ignorance if I’ve misunderstood.

Here’s the thing I don’t understand. Most of Arizona is a long way from the coast, and 4,000 feet above current sea level. Even in Pangea, the land that is currently Arizona was a long way from the coast.

So when, and how, was it ever sea bed? Did ancient oceans rise more than 4,000 feet above current levels? Was Arizona once at a lower elevation, but has been pu8shed upwards from underneath? Some other thing I haven’t thought of?

2

Wikipedia has a breakdown of how the seas came and went, but most recently Arizona was part of the Western Interior Seaway.

3

Pretty good timeline here, starting on page 5. PDF warning.

4

Actually, a lot of the sandstone in Monument Valley and Canyonlands (certainly, the most impressive buttes and mesas) isn’t marine, but aeolian. Fossilized dunes, basically. Much of the rest is river sandbar and alluvial fan deposits, and then the rest is delta and coastal sandbar sands.

Generally, when you have a lot of reddish-orangish sandstone, it’s not primarily marines, but terrestrial.

5

What is the difference between those remaining “stacks” and the eroded flat part? Are those vulcanic vents perhaps?

6

No, they’re sandstone. They’re just all that gets left after everything in between is eroded away. The difference is generally that the remanant parts were the bits between jointing that developed during various geological processes. The bits in the joints were easier to weather and erode, so that’s where water channels preferentially developed and wind and ice and salt did most of its work.

Here are some related papers with nice illustrations of the concept (from your part of the globe, even).

Generally, volcanic remnants don’t form that characteristic mesa shape - look at Shiprock, Chaistla Butte, Agathlan or even Bear Lodge Butte (Devils Tower). You do sometimes get something similar with flood basalts, though. But the rock itself looks completely different.

7

Ah, that makes sense.

8

Thanks for the information, I guessed completely wrong. On the other hand, that would have been a lot of volcanoes in a very small space.
ETA: Nice pictures indeed, I should visit that Elbsteingebirge.

9

December 8, 1941

10

Took me a while :smiley:

11

Too soon.