More evidence that "Rye-o" was a familiar pronunciation:

In a WPA interview conducted around 1939, 91-year-old Ben Kinchlow, a African-American ex-cowboy, recalled that "I fell in love with a Mexkin girl once. They was two of them girls an' they lived on a ranch owned by Ed Daughtery on the Ryo Grand (Rio Grande) an' the caporal (head man) was their father."

The glosses are by the interviewer, Florence Angermiller. Kinchlow is regularly quoted as saying "Rye-o," not "Ree-o."

Different Rio Grande, different occupation, same pronunciation.