As plans for the Coastal and Valley Sectors were finalized, the planners turned their attention toward the Mountain Sector to complete the 93,000-acre Irvine Ranch Master Plan. With Irvine Lake at its center, planning for this 33,000-acre sector would primarily focus on residential land uses, regional circulation, infrastructure, open space and trail systems.
Because of the diverse topography of the Mountain Sector, the predominant form of land use was originally envisioned as a range of residential enclaves with significant concentrations of mid- to high-density housing. Now, approximately 30,000 acres of the 36,000 acres that make up the Mountain Sector are permanently dedicated to open space. The remaining acreage has been set aside for low- to medium-density housing.