I have found several of these guides to be very helpful. In particular, Adventuring in the California Desert, and Adventuring in British Columbia led me to some amazing places I might not otherwise have known about.

Travel Guides

Adventuring in the California Desert, A Sierra Club Adventure Travel Guide, by Lynne Foster

Adventuring in Arizona, A Sierra Club Travel Guide, by John Annerino

Adventuring in the Pacific, A Sierra Club Travel Guide, by Susanna Margolis

Adventuring in Hawaii: Hawaii, Maui, Molokai, Lanai, Oahu, Kauai, A Sierra Club Travel Guide, by Richard McMahon

Adventuring in New Zealand, A Sierra Club Travel Guide, by Margaret Jefferies

Adventuring in the San Francisco Bay Area, The Sierra Club Travel Guide to San Francisco, Marin, Sonoma, Napa, Solano, Contra Costa, Alameda, Santa Clara, San Mateo Counties and the Bay Islands, by Peggy Wayburn

Adventuring in Alaska, The Sierra Club Adventure Travel Guides, by Peggy Wayburn, Jody Horst

Adventuring in the Rockies, The Sierra Club Travel Guide to the Rocky Mountain Regions of Canada and the U.S.A.

Adventuring in British Columbia, by Isabel Nanton

Guides to the National Parks

The Sierra Club Guide to the National Parks of the Rocky Mountains and the Great Plains, by Conger Beasley

The Sierra Club Guides to the National Parks of the East and Middle West, by William A. Blake

The Sierra Club Guides to the National Parks of the Pacific Northwest and Alaska, by Robert Belous

The Sierra Club Guides to the National Parks of the Desert Southwest, by Conger Beasley, James V. Murfin, Irene Pavitt

The Sierra Club Guide to the National Parks of California, Hawaii, and American Samoa, by Joseph E. Brown

Easy Access to National Parks The Sierra Club Guide for People with Disabilities, by Wendy Roth, Michael Tompane

Guides to Natural Areas

The Sierra Club Guide to the Natural Areas of New Mexico, Arizona, and Nevada, by John Perry, Jane Greverus Perry

The Sierra Club Guide to the Natural Areas of Colorado and Utah, Sierra Club Totebook, by John Perry, Jane Greverus Perry

The Sierra Club Guide to the Natural Areas of California, by John Perry, Jane Greverus Perry

The Sierra Club Guide to the Natural Areas of Oregon and Washington, by John Perry, Jane Greverus

Naturalists Guides

A Sierra Club Naturalists Guide to the Southern Rockies, The Rocky Mountain Regions of Southern Wyoming, Colorado, and Northern New Mexico, by Audrey Delella Benedict, Barbara Bash

A Sierra Club Naturalists Guide to the Sierra Nevada, by Stephen Whitney

A Sierra Club Naturalists Guide to the Pacific Northwest, Oregon, Washington, Idaho, Western Montana, and the Coastal Forests of Northern California, by Stephen Whitney

The Deserts of the Southwest, A Sierra Club Naturalists Guide, by Peggy Pickering Larson, Lane Larson, Edward Abbey, Ivy Larson