Only the Clear Lake volcanics in California lie as far west in the coterminous United States. Unlike Clear Lake, Boring lava vents have been inactive for at least 300,000 years.
Boring lava is characteristically a light-gray phyric olivine basalt.
A specimen from Rocky Butte is predominantly labradorite, with phenocrysts of olivine, mostly altered to iddingsite. The volcanoes locally contain scoria, cinders, tuff, tuff breccia, and ash. The topography of the Portland area is varied. The floors of the lower Columbia River Valley and Willamette Valley are nearly flat to gently rolling terraced surfaces. Altitudes range from near sea level in the vicinity of Portland to nearly 400 feet on some of the higher terraces.