See if yuo can find a local social cycling club. SFVBC starts from the front parking lot of CSUN (or at least it used to) if you are in the San Fernando valley. There is a LAB (LAW when I knew them) chapter somewhere in the Santa Monica area, or perhaps hte chapter is wider, but there are ride starts in or near Santa Monica.

For me the huge jump was from 40 to 50 miles. The distance was actually not the issue, it was that I was riding with SFVBC and the in valley rides maxed out at about 40 and the shortest out of valley were about 50. But there was a huge difference in climbing.

If you can find a local club an dalso get advance ideas about the routes used yuo can ride to teh start and then ride with them and cut off to go home. That means some riding alone, but a lot of the miles with a group. And you can adjust the pre formal start miles depending on when you get up. (But if you try this be sure to get to the start by the listed starting time, my experience is cycling groups are one of the few things that start on time, and it can be very difficult to make up even just one minute).