Blue goo is a sticky, plasticky, blueish-grey, clay-textured soil derived from a highly weathered serpentinite mélange.^[1][2] The name derives from the soil's color; a result of undergoing anaerobic conditions and becoming gleyed.^[3] A greyer variation is called "grey goo".^[2] Blue goo is primarily found along the Northern California coast.^[2]

The Franciscan Complex is the bedrock from which blue goo is derived.^[1] It stretches along the coastline from Central California up to Southern Oregon and contains sheared materials from both the Pacific and North American Plates that have accumulated in the accretionary wedge.^[1]

The rock types that produce blue goo include: greenstones, cherts, basalts, shales, sandstones, schists, and serpenitites.^{[1][2][4][5][6]} These materials mixed together forming a "plum pudding" or a mélange.^[1][2] This mélange decomposed through weathering to form blue goo.^[7]

Clay soils like blue goo have the highest water-holding capacity when compared with other soils, giving them a low draining capacity.^[3] This kind of habitat is unsuitable for most plants,^[3] but the Northern California coastline maintains high levels of vegetation year round.

Due to blue goo's clayey texture, it slips when overly saturated.^[6] This slippage is increased in heavy rainfall areas and in shallow soils; deep soils have more total pore space and are not as prone to slippage.^[3] These features contribute to the landslide-ridden environments found along the Northern Californian coast.^[5][6]

The Franciscan Complex, from which blue goo is derived, extends from Central California up the coast through parts of Southern Oregon.^[1] But blue goo has only been found in two Northern Californian regions located in Humboldt County: the Trinidad region and the Orick region. Blue goo is thought to also be found in the Eel River region and along the Southern Oregon coastline.