Parks and Forests:

California State Parks
 
Anza-Borrego Desert State Park
 
Cleveland National Forest
 
San Diego River Park Foundation
An organization dedicated to enhancing the San Diego River and working toward the establishment of a river-long park, from the headwaters in the mountains near Julian, California, to the Pacific Ocean in the community of Ocean Beach in the City of San Diego. The San Diego Sea to Sea Trail will connect with the Park near the headwaters of the San Diego River.
San Dieguito River Park
Is the agency responsible for creating a natural open space park - a 55-mile corridor - in the San Dieguito River Valley. The Park will someday extend from the ocean at Del Mar to Volcan Mountain, just north of Julian. Once both the San Diego Sea to Sea Trail and the SDRP trail systems are finished, they will link up 55 miles inland, forming a giant loop.

Hiking and Trails:

Afoot and Afield in San Diego County
This is a book by Jerry Schad, recognized expert on the Southern California outdoors.  Jerry was also an accomplished astronomical and sky photographer.
Mission Trails Regional Park
Centrally located and only eight miles northeast of downtown San Diego, Mission Trails Regional Park encompasses nearly 5,800 acres of both natural and recreational developed land. There are plans afoot to link the San Diego Sea to Sea Trail with the Mission Trails system via Sycamore Canyon, southeast of Poway.
Pacific Crest Trail Association
The PCT spans 2,650 miles from Mexico to Canada through three western states. It reveals the beauty of the desert, unfolds the glaciated expanses of the Sierra Nevada, and provides commanding vistas of volcanic peaks and glaciers in the Cascade Range. The Trail also passes through historic mining sites and evidence of man’s endless quest for natural resources. The San Diego Sea to Sea Trail crosses the PCT just east of Lake Cuyamaca.
San Diego County Trails Council
SDCTC is an all-volunteer trails advocacy organization. Members include equestrians, mountain bikers, hikers and other individuals and clubs concerned about environmental issues, resource protection and outdoor recreational opportunities.  SDCTC’s goal is to maintain a balance with the environment while encouraging the development of an interconnecting regional trails system linking public and private lands.  With over 20 years of experience, SDCTC’s efforts have significantly enhanced trail development opportunities, environmental and trail education, and advocacy.
San Diego Hikers
San Diego Hikers is a FREE resource where you can find maps, photos and reviews for the best hikes in San Diego.
Trail Organizations in San Diego Country
A "comprehensive approach" to Riding and Hiking Trails is now part of the Trails Strategic Plan for San Diego County's General Plan 2020 planning process. The Plan will derive from a "bottoms-up", community-based approach. This page attempts to list the organizations that will be involved in this planning. Many of the organizations belong to the San Diego County Trails Council, which is "the lead trails advisory organization for other trail groups by providing education, expertise and support for the acquisition, preservation and maintenance of riding, hiking and mountain biking trails".

Desert:

All about the California Desert
 
Anza-Borrego A to Z
A detailed guide to the place names and history of the Anza-Borrego desert region. More than just a place names guide, author Diana Lindsay brings the history of the area to life through entries that chronicle the fascinating people, places, and things that have shaped the region.

Salton Sea Authority


Organizations:

The Nature Conservancy of California
 
National Wildlife Federation
 
San Diego Chapter of The Sierra Club

Education and Programs:

National Wildlife Federation's Connect Kids & Nature
San Diego Natural History Museum
Devoted to the diversity of the Southern California and Baja regions with respect to the environment and nature. Learn about the evolution of the natural world through research, exhibits and education.
San Diego Inner City Outings (ICO)
An outstanding Sierra Club community outreach project that provides positive wilderness experiences for urban youth. Are you looking for something very worthwhile? Here is an opportunity!

Other Resources:

Backpackinglight.com
An excellent site for those into the growing ‘pack light’ genre, and who deplore the consumerism of much of the outdoors equipment industry.
Up-to-date listing of BLM recreation sites in California
Mountain Lion safety information from the California Department of Fish and Wildlife
 
National Weather Service - San Diego
San Diego Area Mountain Top Cameras