Here is a PDF current as of October 2010 of the chain laws across the US & Canada.
California DOT Chain Requirements [web page] PDF of California DOT Chain requirements (revised 11/99)
Starting Sept. 1, all commercial vehicles traveling on I-70 in Colorado between milepost 133 (Edwards exit) and milepost 259 (Morrison exit) must carry sufficient chains to be in compliance with the Colorado chain law. The law requires commercial vehicles to [...]
Both the Colorado Motor Carriers Association and the Colorado Department of Transportation is reminding commercial vehicles that they must carry chains on I-70, about the first hundred miles west of the Denver metro area from Sept. 1 through May 31. [...]