There are
2,698 mi
from San Marcos, CA to Allentown, PA
That's the driving distance. It would take 2 days to go from San Marcos, California to Allentown, Pennsylvania.
The flight distance (direct flight from San Marcos, CA to Allentown, PA) is 2,337.73 mi.
2,698 mi = 4,341.61 kms