Geology

<--Portland Hill Silt

Boring Lava Basalt-->

Columnar Basalt (My Geology Professor)

Entablature Basalt Formation

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		Geological Field Trip Road Log October 20, 2002 9:05 am Leave Sylvania Campus of PCC Mile 0 9:10 am Summit of Mt. Sylvania Mile 0.5 Mt. Sylvania is a vent from the Boring Lava, about 1 mya. It is a small shield Volcano. The basaltic flows have been covered with deposits of Portland Hill Silt, which is fine-grained wind-blown deposit sediment. Late stage flood sediment. When Portland Hill Silt gets wet it will slide downhill and take any structures with it. 9:45 am Construction site on Barbur Blvd and SW 53rd Mile 2.5 Excavation of Portland Hill Silt. Elevation 550ft. Demonstration of the dilatency of Portland Hill Silt. When Mr. Lawes gathered some wet Portland Hill Silt and shook it in his hand, to demonstrate the latency, the water floated on top of the Portland Hill Silt. Portland Hill Silt is more stable when at 90� instead of a smaller angle.

	10:00 am Basalt Rock on Side of Road Mile 2.7 Basaltic Andesite composed of feldspar and mostly olivine. Weathering and construction has exposed the Basalt 10:18 a.m. Across Barbur Blvd from concrete retaining walls Mile 5.15 1996 floods created a land slide on Barbur Blvd at approximate 7600 SW Barbur Blvd. In order to protect the houses that are built at the top of the landslide area a concrete retaining wall was built. Steel rods were set back approximately 50 feet to be lodged into rocks in order to create a stable retaining wall, which will hold back the Portland Hill Silt in another flooding episode.

	10:37 am Marquam Park Mile 9.0 Columbia River Basalt - Columnar formations lower and entablature formations higher. CRB covers Eastern Washington, Northern Oregon and Western Idaho covering 63,000 square miles. The flows occurred 13 to 15 mya. West hills of Portland have basalt base covered by Portland Hill Silt. West Hills fault from compression of plates. We found some basalt with vesicles and some basalt with amigoloids. Elevation 350ft

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