Depends on where you look. The basalt on the Olympic Peninsula ranges from 50 to 60 million years old, whereas the basalt from the Columbia Plateau erupted from 5 to 17 mya (primarily around 16 mya). Granite in the area also range widely in age, with some very young, and some such as Mt. Stuart, which solidified around 93 mya. Not sure if this answers your question or not but hope it helps.
The rocks at Alki range include the 23,000 to 28,000 sediments exposed at low tide at Mee Kwa Mooks sediments and the 27mya Blakeley Formation rocks. I don't think there's any granite or basalt there?
I love this post thank you. I've been to, over or around these formations a number of times on bike rides but will henceforth view them differently.
As a young rock climber living in Seattle I quite resented the absence of exposed rock. Being surrounded entirely by gravel was frustrating. Nowadays, being able to go tread on some 42 million year old volcanic sediments is nearly as exciting. I mean... how far down does the formation go? It must be, after all, the "tip of the iceberg". And these pairs of formations... because the Duwamish used to flow between them?
Are all rocks in the area roughly the same age? Granite vs basalt?
Depends on where you look. The basalt on the Olympic Peninsula ranges from 50 to 60 million years old, whereas the basalt from the Columbia Plateau erupted from 5 to 17 mya (primarily around 16 mya). Granite in the area also range widely in age, with some very young, and some such as Mt. Stuart, which solidified around 93 mya. Not sure if this answers your question or not but hope it helps.
As far as alki beach specifically
The rocks at Alki range include the 23,000 to 28,000 sediments exposed at low tide at Mee Kwa Mooks sediments and the 27mya Blakeley Formation rocks. I don't think there's any granite or basalt there?
I love this post thank you. I've been to, over or around these formations a number of times on bike rides but will henceforth view them differently.
As a young rock climber living in Seattle I quite resented the absence of exposed rock. Being surrounded entirely by gravel was frustrating. Nowadays, being able to go tread on some 42 million year old volcanic sediments is nearly as exciting. I mean... how far down does the formation go? It must be, after all, the "tip of the iceberg". And these pairs of formations... because the Duwamish used to flow between them?
Sophie Bass' book is a great narrative of Seattle. Seattle with all its faults is still geologically fascinating! (See you at the MOHAI next month!)
I assume that your use of faults was a nice geological play on words!
OH ABSOLUTELY!!