The Boring Lava Field shows a similar composition to the High Cascades that run through Oregon and southern Washington state, with Pliocene to Pleistocene basalt lava flows and breccias. It was active during the late Tertiary into the early Quaternary. Within the field, lava shows a diverse composition overall, varying from low-K, tholeiitic to high-K, calc-alkaline eruptive products. Some of the low-K tholeiite deposits likely originated from vents closer to the High Cascades, and they are overlain by Boring Lava materials. J. M. Shempert proposed that mantle sources for the two different lava types may be different and that the calc-alkaline sources are more refractory.