Fieldbrook is very nearly on the north bank of the Mad River, which flows into the Pacific Ocean between Arcata and McKinleyville. Although the Mad River supplies the water to much of Humboldt County's population, that small population does not have a significant impact on the river's flow. The north side of Fieldbrook Road is second-growth (coppice, multiple thinner trunks sprouting from the stumps of harvested trees) redwood forest with the occasional clearing for a house, and the logging rules allow the forest canopy to maintain a height of . A narrow zone adjacent to the road is maintained as an unlogged buffer, presenting the illusion of virgin forest to tourists, but even on the north side of the buffer, in any given year the majority of the timber tracts have been growing for at least seven years, comprising a wilderness if not exactly parkland. The region abounds with wildlife and residents routinely find deer and elk grazing in their yards, foxes and raccoons digging through their garbage, the occasional black bear or cougar.