Four Craters Lava Field eruptions from the field were accompanied by a slight sinking of the older rock surface. This shallow, graben-like sink is about 3 kilometers wide and extends to the south into an old lake basin. Crack-in-the-Ground marks the western edge of this small, volcano-tectonic depression and is nearly 9 meters deep and over a meter wide. The crack is the result of a tension fracture along a hingeline produced by the drapping of Green Mountain lava flows over the edge of upthrown side of the concealed fault zone. Four Craters Lava Field Four Craters Lava Field is a basaltic volcanic field
Boring Lava Field Boring Lava Field The Boring Lava Field (also known as the Boring Volcanic Field) is an Plio-Pleistocene volcanic field with cinder cones, small shield volcanoes, and lava flows in the northern Willamette Valley of the U. S. state of Oregon. Located southeast of downtown Portland, the field got its name from the town of Boring, Oregon, which lies just to the southeast of the most dense cluster of lava vents. The zone became active about 2.7 million years ago, with long periods of activity interspersed with quiescence. Its last eruptions took place about 57,000 years ago at the Beacon Rock