I've found some diagrams of the Oregon Coast Range, but they are very basic. An friend said he thinks there is limestone deep underground, but my understanding of the formation of these mountains is that there is not. Where can I find information to settle this question? (or, if you know the answer, I'd be glad to hear it)
$\begingroup$ At USGS they say there are mudstones: "Marine mudstone and sandstone are interbedded with all of the volcanic units and comprise most of the late Eocene to Miocene stratigraphic section that forms the flanks of the Coast Range uplift." pubs.usgs.gov/of/1995/of95-670 $\endgroup$– user12525Jul 1, 2019 at 7:13
I'm not familiar with the Oregon Coast Range, but limestone is such a ubiquitous and widespread rock that your friend is almost certainly right. For strata to be limestone, they need to have been under the sea when they were laid down. The fact that some are found today near the tops of mountains only means that plate movements have uplifted them since they were formed. They might easily have become overlaid with igneous rock, volcanic tuffs, sandstone etc,but if you go down deep enough the probability is that you'll find limestone somewhere. You usually don't have to go down very far, and there are usually exposures that reveal it. Limestone (calcium carbonate) is often a good place to find fossils.
1$\begingroup$ The OP specifically asks about the Regon Coat Range. Since you are "... not familiar with the Oregon Coast Range..." I would propose that your response should have neen a Comment rather than an Answer. $\endgroup$ Jul 1, 2019 at 20:08