Totally doable - although that's going to eat up at least 1/2 of the weekend :-) Of course, it also depends on what part of L.A. and what part of San Diego. There could easily be 25 miles difference there. You take the 1st half of the 70 mile LA River Ride down to Long Beach, and then you cut down 15 miles to Irvine and then The Amtrak Century covers the rest of the distance. 150 miles get you from Griffith Park to Petco Park.