The High Cascades, a segment of the Cascade volcanic arc that includes the Boring Lava Field, is characterized by basaltic lava flows with andesite, tuff breccia, and volcanic ash. The High Cascades may lie over a graben (a depressed block of the Earth's crust bordered by parallel faults), and activity at the Boring field and throughout the Portland area may be associated with deformation of the block. Portland lies within the Portland Basin, part of the forearc (the region between an oceanic trench and the associated volcanic arc) between the Cascades major arc and the Pacific Coast Ranges, which consist of Eocene to Miocene marine sedimentary rock deposits and Eocene intrusions and extrusions of basalt that were emplaced on the Siletz terrane. The eastern boundary for the Portland Basin is the Cascades, while the Tualatin Mountains lie to the west, along an anticline formation that has been changing since the Miocene. The Boring Lava Field sits on the floor of the Portland Basin, residing in the forearc setting between tectonic extension to the south and compression to the north. The uneven distribution of vents within this forearc suggests a local zone of crustal expansion, indicative of northward movement and clockwise rotation of a tectonic microplate that leads to gradual northwest-trending propagation for the field over time. The migration rate for volcanism within the field is an average of ± per year relative to the motion of crustal blocks in the region, using the last 2.7 million years as a starting reference point. The Boring Lava Field represents the youngest episode of volcanism within the Cascade forearc, and while there is no evidence that they were associated with a slab window (a gap that forms in a subducted oceanic plate when a mid-ocean ridge meets with a subduction zone and plate divergence at the ridge and convergence at the subduction zone continue, causing the ridge to be subducted), they likely interacted with the regional mantle wedge.