I tried to do a little research on the subject matter of this postcard before posting. I came up short. My best guess is that “Saltwater” was the name of an Indian clan who made their home near a lake in New Mexico, whose water was salty.
What easily came up in my search, was all the places I could purchase a similar postcard. The first one was $9.99 + $4.99 shipping. Crazy, Man!