The detector description code for tracker is in the detc file, directory dtgeom and the related TZ titles constants in the cmz file //titl directory tgeom13.
The HITS recording in CMSIM step is a common procedure for both tracker and muon hits and the code is in cmsi file directory cmstep routine cmthit.
The TRAK file contains tracker simulation specific code in the following directories:
trbase Basic tracker routines
trutil Various tracker code utilities
trdigi Digitization simulation code
trfind track finding
trfits track fitting routines
trvertx vertex finding and fitting