GR translation: who was crossing the great Rio forever

[Mike Jing]

V69.10-13, P70.28-31   Whappo is wearing chaps of imported gazelle hide
that Crutchfield bought for him in Eagle Pass from a faro dealer with a
laudanum habit who was crossing the great Rio forever, into the blank
furnace of the wild Mexico.

What does it mean for the faro dealer to be "crossing the great Rio
forever"? Did he actually cross it, or was he forever in the process of
crossing it?