There are
2,627 mi
from Gaithersburg, MD to San Marcos, CA
That's the driving distance. It would take 1 day 23 hours to go from Gaithersburg, Maryland to San Marcos, California.
The flight distance (direct flight from Gaithersburg, MD to San Marcos, CA) is 2,249.50 mi.
2,627 mi = 4,228.44 kms