The Mists of Avalon by Marion Zimmer Bradley (1983) — Bradley lived near Mendocino while writing this Arthurian retelling from the women's perspective. The coastal fog and the sense of an ancient world half-visible through modern life seep into the book in ways that are unmistakable if you've stood on the Mendocino headlands in the morning.
The Bell Jar is the wrong book, but Sometimes a Great Notion by Ken Kesey (1964) is exactly right. Set on the Oregon coast but rooted in the same logging culture that built Mendocino, it follows a stubborn logging family fighting the union and the river and each other. Nothing better captures the character of the small coastal lumber towns that lined this coast, and Mendocino's Victorian buildings are the physical legacy of the world Kesey describes.
The Log from the Sea of Cortez by John Steinbeck (1951) — Steinbeck's account of a marine biology expedition down the Baja coast is ostensibly about tide pools and sea life, but it is really a meditation on observation, science, and what it means to look at the natural world honestly. The tidal ecology of the Mendocino headlands — the same pools, the same cormorants — will look different after reading it.
Season of the Witch: Enchantment, Terror and Deliverance in the City of Love by David Talbot (2012) — This history of San Francisco in the 1960s and 70s illuminates the cultural moment that drew artists and counterculture figures north to Mendocino. Understanding why the town became an arts colony requires understanding the Bay Area scene they were partly escaping.
The Wilder Shore by David Rains Wallace (1984) — A naturalist's account of the California coast, covering the ecology of the headlands, the redwood forests, and the marine environment. It is the best single book for understanding what you are looking at when you walk the Mendocino bluffs.