I would make sure you get a thorough check out in mountain flying operations. Some of the suggestions here, while well intentioned, could be deadly in a C-152 if the density altitude is too high. I've got hundreds of hours of low level search and rescue flying in southern California and would not attempt taking a C-152 through the Banning Pass or over the Cajon Pass unless conditions were ideal. The number of wrecks on both sides of those passes is unbelievable.
You can easily get into a situation where the downdrafts exceed the climb capability of the aircraft near some of those mountains.
Typhoonpilot