Are the gravel roads sheltered at all? If so, this will be closer to an MTB than a road ride, and you will need LESS clothing as you will be working harder. When I go out in the woods in these temps, I wear a baselayer, thermal or wool jersey and winter cycling jacket (wind layer) on top, knickers, knee-high wool ski socks and GORE tights on the bottom, winter cycling shoes (the Pearl Izumi are the best), a skull cap (I can't STAND a balaclava) with my helmet, and lobster claw gloves with wool liners.

The important thing is that if you start to sweat, you MUST remove a layer or unzip or otherwise regulate your temp. Getting wet will be your undoing. Sweaty feet and hands tend to be my issue, so those get wet and then get cold.

As for the CamelBak - put it under your jacket if you can. The hose will definitely freeze. I've tried blowing the water back into the bladder, but the bite valve freezes pretty solid, leving you with no hydration. Insulated hoses will also help (but not always prevent the bite valve freeze issue). Putting some coffee into an insulated bottle isn't a bad thing either (or, last night, the boys added some *ahem* antifreeze of the alcoholic variety to their water .

Enjoy it and have fun. If you are dressed right, the 35 miles won't be a problem. I've been out already for 3 and 4 hour rides in 20F temps, and it's only going to get colder.

SheFly