There are
983 mi
from Thornton, CO to Rancho Cucamonga, CA
That's the driving distance. It would take 17 hours 7 mins to go from Thornton, Colorado to Rancho Cucamonga, California.
The flight distance (direct flight from Thornton, CO to Rancho Cucamonga, CA) is 801.15 mi.
983 mi = 1,581.80 kms