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  • Marisa Acosta

Field Trip 2019




I was able to tag along on a field trip led by Marli Miller for her Structural Geology Class this previous weekend. I learned a lot and saw MANY cool rocks, briefly summarized below



Circular holes in serpentinite/ blueschist, perhaps from boring clams? Incipient tafoni?

Curved slump scarp of the Cape Blanco marine terrace & the 1867 Cape Blanco lighthouse.


Excellent outcrop of the fluvial gravel (middle, dark layer) below marine terrace sandstone (top layer with trees) both overlaying the fossiliferous Floras Lake sandstone.

Some amazing sea stacks near Sisters Rocks State Park (pull off near milepost 315 of the 101 and walk over pebbly mudstone and gritstone)

Type locality of the Otter Point Formation - Jurassic member of the Gold Beach terrane in the Franciscan complex. Note vertical beds (turbidite sequences with limestone strata) overlaine by a marine terrace. Note the halite precipitating from the ocean water on the outcrop and the neat limestone weathering patterns.

Rainbow Rock! My favorite stop of the trip. Saw some sea life , and some astonishing radiolarian chert with siltstone interbeds. The outcrop here displays textbook flexural slip - where the rheologically weak siltstone deformed preferentially w.r.t. the rheologically stronger chert strata. Also , some amazing sea caves and foggy views of the coastline.

Camping on the Rogue River (one of the neatest rivers in Oregon because it drains the Klamath belt). Saw some trilium, chrysotile veins lined with magnetite in partially altered Josephine peridotite provenance cobbles, and some cute, really weird-looking mushrooms growing on the Redwoods.

Tribute to the Redwoods.

Stopping at the Rough & Ready wayside near Cave Junction - more Josephine ophiolite cobbles in a stream. Because the Josephine forms ultramafic soils, the plants that grow on it are not the same one would see elsewhere in Oregon.


Last stop was at the Oregon Caves! In the Siskiyou mountains, this cave is a solution cave formed in marble of the Applegate group of the Rattlesnake Creek terrane. We saw all of the typical limestone precipitate structures (moon milk, soda straws, popcorn, stalactites, stalagmites, columns, drapery, bacon, etc.)



University of Oregon

Department of Earth Sciences

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