Can someone recommend a summit with a long class 3 section accessible within a 3-hr Drive of Los Angeles? Thanks very much

My favorite long class 3 climb is Middle Palisade. Only the approach is really long. I think most people backpack in and then climb the peak and hike out next day. But I've seen reports of people doing it in a day -- they're animals!

Not a long section, but Strawberry Peak is very close to LA.

https://modernhiker.com/hike/hiking-strawberry-peak

No shade and no water, so if it's warm weather, take a good 3-4 liters.

Spanish Needle in the Southern Sierra.
http://www.summitpost.org/spanish-needle/153267

Ooh, I like the look of this. You been there Gold Scott?

I did Spanish Needle, Rockhouse Peak, and Owens Peak last Tuesday, Wednesday, and Thursday. It doesn’t take much bushwhacking or side-hilling on loose crap in hot weather to make me wish I were further north where the peaks are higher and more enjoyable. Rockhouse was the best of the three. I was only there to finish the “Southern Sierra” peaks in the Sierra Club SPS list.

I lived in Inyokern (directly across from Owens) for 7 years, and would never dream of doing those peaks in June - too damn hot. Lots of fun from November thru March, though.