Remember this? It's coral strata from the Pacific Coast off San Francisco.
I would bet that the numbers for the depthe of the Pacific seabed should be adjusted upward to correct for the uplift on the edge of the Pacific Plate (there are credible estimates that the Santa Cruz Mountains would be twice as high as Everest but for the rate of erosion), so perhaps your 450 ft estimate isn't far off.
Highway 17 would sure be a lot more exciting. We still have much to learn.
Dr Stephen Oppenheimer, in his book Eden In The East explains how most of these depths based on coral reefs are incorrect.