There are
2,558 mi
from San Marcos, CA to Niagara Falls, NY
That's the driving distance. It would take 1 day 21 hours to go from San Marcos, California to Niagara Falls, New York.
The flight distance (direct flight from San Marcos, CA to Niagara Falls, NY) is 2,162.35 mi.
2,558 mi = 3.22 kms