Going from 4 miles to 30 is a big jump. So is going from 10 miles to 30. I'd suggest doing the 10 miler and then continue to gradually increase your miles from there. You'll be ready for a 30-miler soon, I promise. Hopefully, they'll be happy to invite you for their group rides then.

IMO, it's better to build up your mileage gradually than to get discouraged from trying to do a ride you're not quite ready for. I wouldn't necessarily count--at least not without a map--being to head back on your own if you're not familar with the area.

Good luck!

And p.s. I started off where you are now and ended up doing a 160-mile one day ride about a year later, so if you establish some goals, I promise that you you can exceed your wildest expectations.