Question

I recently read Carl Ortwin Sauers' The Early Spanish Main, 1966

On page 64 was an odd mention of the following:

"There is evidence also of an earlier presence of people of advanced culture that differed from that of the Arawaks. The first such indication is the elaborate irrigation works that were seen in and about the region of Xaragua in arid south-western Espanola....A second is the Minas Viejas of the San Cristobal mining district in which Columbus thought he recognized the mines of Solomon."

What did these two features actually turn out to be?