calendar-mark-1 is a compiled Lisp function in `diary-lib.el'.

(calendar-mark-1 MONTH DAY YEAR FROMABS TOABS &optional COLOR)

Mark dates in the calendar conforming to MONTH DAY YEAR of some system.
The function FROMABS converts absolute dates to the appropriate date system.
The function TOABS carries out the inverse operation. Optional argument
COLOR is passed to `calendar-mark-visible-date' as MARK.