I can vouch for Catalina. It's a PITA to join their Conservancy Club (mandatory to get a 1-year MTB license), and you can't ride anywhere you like--only on the fire roads, not the hiking trails.
But it's pretty spectacular. I rode from Avalon to Parson's Landing and back in one day: over 80 miles, and about 12K feet plus in climbing. It's not great for "real" mountainbikers, but it's perfect for roadies on a MTB, like me.

You'll see maybe 2-3 tour jeeps, and the same ranger once or twice all day. A perfect post-Ebola playground.