The 25 Hours of Thunderhill is an endurance racing event held annually during the first weekend in December in Northern California, at the Thunderhill Raceway Park; just outside the small town of Willows. The race is longest road event on a closed course in the United States.

It has been run since 2003,[1] sanctioned by the National Auto Sport Association.[2] It is the successor to the Timex 12 Hours of Thunderhill event run between 1998 and 2002.[3]


  1. ^ "25 Hours of Thunderhill – Past Results". Retrieved 22 February 2017.
  2. ^ "Davidson Racing Norma wins the 25 Hours of Thunderhill". 2014-12-07. Retrieved 22 February 2017.
  3. ^ "History of the 25 Hours of Thunderhill" (PDF). NASA 25 HOURS OF THUNDERHILL. Retrieved 22 February 2017.