Boring Lava Field subsurface regions near Aurora and Curtis, and these intrusions have been associated with normal faulting at Parrett and Petes Mountain, Aurora, Curtis, and Swan Island (along the Molalla River). Faults together with igneous intrusions are usually accompanied by stretching and doming as a result of magma influxes or collapses from the evacuation of the magma flows. Similarly, faults north of Oregon City might have resulted from subsidence after magma chambers emptied or lava was extruded as a result of Boring Lava eruptions. Some of the Boring lava vents are known to truncate hydrogeologic units in the surrounding area. Eruptive vents
Boring Lava Field Quaternary, in what is now the Portland area as well as the surrounding area, with a particularly concentrated pocket of activity to the east. Nearly all of these eruptions were confined to single vents or small vent complexes, with the exception of a lava plain southeast of present-day Oregon City. Boring Lava generally consists of flowing lava; only one eruptive deposit contains tuff, ash, and tuff breccia, and one vent to the northeast of the Carver area displayed evidence of explosive eruptions that later became effusive. According to the United States Geological Survey, sometime less than 100,000 years ago, magma