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 of Troutdale and more than 32 vents within a radius of Kelly Butte. Mostly small cinder cone vents, these volcanoes also include some larger lava domes from shield volcanoes at Mount Sylvania, Highland Butte, and Larch Mountain. The Boring Lava Field marks the densest volcanic vicinity in this group, with 20 volcanic vents encompassing an area of . It includes more than 80 known small vents and associated lava flows, with more volcanic deposits likely present under sedimentary rock deposits from the Missoula Floods (also known as the Bretz or Ice Age Floods), which took place between 21,000 and 15,000