The West Hills and The Boring Lavas

The hills of West Portland are part of a rich tapestry of geologic history that can be found with just a little digging. The area lies on top of the Portland hills silt. The Portland hills silt was the layer formed during a glacial period. sediment called loess (which is wind-blown sediment) was built up on top of other layers.

An interesting sidebar about Portland Hills: there area a number of faults near the hills like the "zoo" fault and the Washington park fault. Geologists can tell these are places where there was faulting or folding because of changes in the nearby rock layers. These are clearly visible when you are in the Zoo max tunnel where there are clear samples of the different layers of rock.

Another interesting geologic feature of Portland is called the Boring lava floes. There is about 90 formations/vents within a 20 mile radius of Troutdale. They are small cinder and shield volcanoes. Many of them are now features of everyday Portland life such as Mount tabor where there are basketball courts and other attractions.

There are a few locations where the formations have been eroded and you can see the actually layers. such a location can be seen on the I-205 freeway. The large scale Missoula floods were the mechanism for the erosion.

Wouldn't it be a fun challenge to visit every one of the 90 formations in Portland?