I habe taken the ATSF route out of Union Station once.
ATSF ran the TEXAS CHIEF to Galveston until 1968. Galveston did have engine facilities.
HBT did have a roundhouse a few miles east of Union on the joint MKT and MP line. But ATSF did have its freight worked to the south of town. Good question about where in Houston ATSF serviced its steam.
BTW, the ATSF line Galveston to a point inside the state of Oklahoma was built and ranby a company mainly owned by Galveston County! Long story.......