Adding to the previous comment.
The Tejon Ranch Company owns 270,000 acres (422 square miles) along the northeast side of I-5 in the Grapevine area, a piece of land nearly as large as the City of Los Angeles, and 40% the size of Rhode Island.
In 2008, the TRC negotiated a conservancy agreement with 5 environmental organizations to protect from development up to 240,000 acres.
The TRC website has regional a map of the larger area. The Windwolves Preserve and the Los Padres National Forest lock up the lands west of I-5.
I think these private and federal lands would be major obstacles to acquiring land to build HSR tracks anywhere near the I-5 corridor.
Tejon Ranch Company-About Us
TRC regional map