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Here a WW I Cavalry unit appears to be coming from the west on Houston street and turning north on Alamo street.  Another army formation appears to come from the east on Houston street to turn south on Alamo.  This suggests to me a parade route that assembled on Houston Street east of Alamo street..  When the parade began the units proceeded west on Houston to Alamo street.  There they turned left on Alamo continuing to Commerce street.  There they made a right turn and continued west on Commerce Street to maybe St Marys (or Flores).  At that point  they made a right turn and continued to Houston street..  They then made a right turn heading east on Houston street.  When they reached Alamo street they turned left heading north for several blocks where they were disassembled.

 Ed Arnold took this and other pictures from an upper floor of the Post Office.  The buildings on both sides of Houston still stand today, but would not be recognized because of cosmetic changes in their facades.