Los Trancos Open Space Preserve is a 274-acre open space preserve, located in San Mateo and Santa Clara Counties, California, near Los Altos Hills, California. The preserve contains about 5 miles of hiking trails, of which 2.1 miles are open to equestrians, and none are open to bicycles. The area was once a part of a 13,300 acre rancho. The preserve's acreage was purchased by state senator Louis Oneal in the early 1900s, who raised horses there. It was sold to a developer in the 1950s.