Before the concept of a Mountains to Sea Trail System, RJM Design Group assisted the City of Irvine; the County of Orange, Harbors, Beaches and Parks; California State Parks , and The Irvine Company in the planning and regional development of a connected trail system for the northern and southern open space areas. It is now called the Irvine Ranch Wildlands & Parks (formerly known as the Irvine Ranch Land Reserve) and has been marked as a "National Natural Landmark," making it the first site in California to receive NNL designation since 1987.

This area includes:

• Limestone and Fremont Canyons, in the northern section of the Irvine Ranch in unincorporated county territory
  
• Peters Canyon Regional Park, near the City of Orange and maintained by the County of Orange
  
• Crystal Cove State Park and Laguna Coast Wilderness Park which form a vast, contiguous open space system stretching between the Cities of Newport Beach and Laguna Beach and extend inland along Laguna Canyon Road.
  
• Bommer Canyon, a key part of the City of Irvine's Southern Open Space Preserve
  

The Irvine Southern Open Space Reserve is an extremely valuable part of the City of Irvine open space plan. This is an integrated network of parks connected by a greenbelt trail system for cyclists, hikers, and equestrians. The priority in this project is habitat preservation, such as San Joaquin Marsh, with trail connectivity and passive recreation of secondary importance.

Citizen involvement, in the form of the Irvine Southern Open Space conceptual Master Plan Committee, was an essential part of the planning process for the project. Through this process the committee consistently emphasized the key priorities for the Southern Open Space: preservation; access; and passive uses consistent with preservation such as trail use, interpretation, education, and picnicking.