Here are some useful URLS. You'd want the same for Nevada as well as you can easily go back and forth between the two states up in the sierras. I personally have not seen 4X4s putting on chain. They tend to be let through at controls but you might want to purchase a set and bring it so you can prove that you can use it if necessary. Check your X5 manual too.

California Road Conditions:
Road Conditions

Webcams of key areas -- very handy!
Caltrans :: Live Traffic Cameras

The stated regulation from the above page:
Chain Requirements:

• R1: Chains, traction devices or snow tires are required on the drive axle of all vehicles except four wheel/ all wheel drive vehicles.
• R2: Chains or traction devices are required on all vehicles except four wheel/ all wheel drive vehicles with snow-tread tires on all four wheels.
  (NOTE: Four wheel/all wheel drive vehicles must carry traction devices in chain control areas.)
• R3: Chains or traction devices are required on all vehicles, no exceptions.