Accuweather.com shows 56/27 Friday, 51/27 Saturday, and 54/18 Sunday.
Weather.com shows 57/31 Friday, 47/29 Saturday, and 47/31 Sunday.
Figure on about 5 degrees colder due to the elevation, and with a buffer for comfort, preparing for single digits is wise - but that doesn't mean we'll actually get to single digits.
As someone who has had to leave early from a cold-weather group hang once in the past (in this case because the dogs couldn't handle the temperatures), I'll tell you it's way better to try it and have to give up, than to never have tried. Remember, this is car camping - the absolute worst case scenario is that you burn some dead dinosaurs to get yourself warmed back up. There will be a lot of people here with a lot of options for gear to borrow and help keep you warm. We'd hate to see you miss the hang on a "maybe".