Please be warned, this is a tough ride! You're not riding on the Green River Santa Ana River Trail here! There is a LOT of dirt, that's the point. On the 100 mile ride, it's going to be technical as well. The 100 and 50 kilo routes don't have as much singletrack, but they're still going to have a lot of elevation, and a lot of dirt. Be prepared! If you're not sure about doing it on a road bike, pre-ride some of it and find out! If still not sure, hop on a MTB with some fast tires (Thunder Burts are my fave) and ride that!
Also, the forecast for Saturday is mid 80's! Carry lots of water, refill at the SAG stops, and be aware where public water is available or stores you can buy some at if needed.