The hill I live on first oozed and erupted as lava from the ocean floor, hardening into basalt more than thirty million years ago. Geologists call the volcanic pimples that rode in and crashed against North America the Siletzia Volcanics, after the modern name of Oregon’s Siletz River, thus compressing time and place. Locked against the continent from Oregon to Vancouver Island in British Columbia, Siletzia is being crushed like newspaper by the inexorable conveyor belt of plate tectonics. Our built environment perches here, small and ant-like.
Over tens of millions of years, basalt becomes soil. Rocks bake, moisture freezes and thaws in the cracks, bursting them open. Rainwater washes the rock with acids liberated from dead plants and the rock itself, peeling layers off like onion skin. Particles pile up into colluvium: a collection, dragged by gravity to the lowest available resting place. Some bits are carried away as alluvium, spread out by creeks on floodplains and deltas. Or the wind does the work, creating aeolian soil. On shorter time scales gophers, moles, and ground squirrels go about their subterranean business and aerate tons of soil. Microbes and plants change its chemistry and texture. On a frosty morning, I watch soil form as stones and rock chunks randomly roll downhill when the sun thaws ice crystals in the weathered rock.
In the taxonomy of soil, Siletzian basalt begets a silty clay loam. The dominant notes are clay and silt – the smallest possible soil particles – with a backbone of sand, whose particles are as big as boulders in comparison. When clouds roll in from the Pacific they rise over the Oregon Coast Range, the first mountains to harvest the rain. Our soil is a water-holding champion, able to soak up six inches of water for every foot of soil depth.
I step outside in winter when the air is heavy with humidity and fog. An overpowering yet sweet, soft aroma rises up from the ground then: an undercurrent of earth mixed with decomposing conifer needles and berries. The berries are long gone, yet that is what I smell.