Heritage Oaks Park is located at the intersection of McKenzie Avenue and Portland Avenue in south Los Altos. It backs up to Permanente Creek (along Miramonte Avenue). At slightly over 5 acres, it is not a large park but it has everything one would want in a neighborhood park. There is a large grass area that plays host to many soccer clubs, touch football and frisbee games. The picnic and grilling areas are nice (and always clean). If you have small kids, the two play areas (and creek) will keep them occupied and the restrooms come in handy when the kids are done mucking about.
Here is a quick aerial tour of Heritage Oaks Park: