Environmental science



Detailed Geological Trip Report


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Detailed Trip Report: First Part

7:45 a.m. We departed from Campus.

We drove north on Highway 101. As we continued north through the Highway, we passed through Yachats, a town that is approximately 75 miles. Just on the left past the Adobe Motel was the turn-off to Smelt Sands Beach which was our first stop.

Stop 1: Smelt Sands Beach.

Smooth and brown rocks are molded together by wet beach sand. The sand is however coarse with contents including, quartz, basalt, shell pieces, serpentine and agates. The rock forming the base rock formation is present in the sand signifying the rock is broken down by erosion.

Different rocks are also exposed and are believed to be from the Cenozoic Era. They are featured as part of the Yachats Basalt and are Late Eocene (36-40 million years) in age. These rocks were formed as a result of the cooling of magma from a series of eruptions (Alt and Hyndman 1978).

There is the existence of a Pleistocene terrace where the town of Yachats is built on. The terrace which was probably formed when the sea level was lower and its deposit is 10,000 to 1.8 million years old. It cuts into the Yachats basalt sequence (Snavely, 1980). Its present level which is above the present sea level is attributed to either the rise of land due to tectonic activity or dropping of the sea level. It is however difficult to know where the uplift of the land is possible in such an active coastline.

Stop 1a: Cape Perpetua-Heceta head area.

There is a trail down the Devils churn at the end of the low road. The existence of local vents in the Cape Perpetua-Heceta head area is the primary sources of basalt in here. They formed shield-like accumulations composed of sub aerial basalt which were initially erupted on a shallow shelf (Snavely, 1980). This explains why basalt is the most common type of rock in Oregon (Alt and Hyndman, 1978).

We departed Smelt Sands Beach.

Stop 2: Strawberry Hill.

This area has interesting erosional patterns as compared to any other area. We observed a series of basalt intrusions that run parallel to each other. Another noticeable formation was running near the path leading down to the beach and down the length of the hill. Regular and brick-like shapes formed the surface of this formation am of the ocean cuts through this basalt flow.

As much as these flows look like sills (igneous body that intrudes parallel to existing rock layers), they are dikes (feature that cuts across the preexisting rock layers). Both the sills and dikes are flat and igneous intrusions to rocks.

The sand in this place is dark and fine-grained most probably because it is wet. Shell midden, which are remains of shellfish is caught and shelled by the natives and not that uplifting of a fossil bed lie around this area.

Stop 3: Heceta Churn (“Devil’s Elbow”).

The erosion of a fault in flows of the Yachats basalt is responsible for the formation of the churn. Basalt and silica-rich basaltic rock form the dikes in this area (Snavely, 1980). Huge and visible basalt formations that were earlier attached to the mainland were separated when erosion of the softer rock around the stacks occurred.

The sand in this area is black since it may be composed of basalt. Black sands in these regions are said to contain minerals such as, garnet zirconium, small gold deposits, titanium, platinum, chromium and iron (Snavely, 1980). A small igneous intrusion as compared to that at Strawberry Hill runs down into the water. The basalt formations cooled slower on the inside but faster on the outside hence gas was released (Carver, Clague & Darienzo, 1997). This explains the large vesicles of the basalt formation on the dikes.


Alt, D. D. & Hyndman, W. D., (1978). Roadside Geology of Oregon. Mountain Press.

Browning, M. & Gallob, J., (1999, March 20). Clearcut’s Role Questioned in Highway Failure.

News Time. Retrieved fromĀ http://www.newportnewstimes.com/1999/nt_news1229/general/nt_news-04.html

Carver, G., Clague, J., & Darienzo, M., (1997). Estimates of Coastal Subsidence from Great

Earthquakes in the Cascadia Subduction Zone, Vancouver Island, Washington, Oregon,

and Northern most California. Department of Geology and Mineral Industries.

Snavely, P. D., MacLeod, N. S., Wagner, H. C. & Lander, D. L., (1980). Geology of the West-

Central Part of the Oregon Coast Range. Department of Geology and Mineral Industries.

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