There are
2,698 mi
from Allentown, PA to San Marcos, CA
That's the driving distance. It would take 2 days to go from Allentown, Pennsylvania to San Marcos, California.
The flight distance (direct flight from Allentown, PA to San Marcos, CA) is 2,337.73 mi.
2,698 mi = 4,341.85 kms