It seems they were content to colonize this region only. Surely they contemplated the possibility of more fertile lands to the south with larger populations ripe for raiding and trading.
Hi, not discouraging more answers here, but thought you might be interested in a few earlier threads; /u/textandtrowel addresses this question here. The first two posts are still open, so feel free to post follow-up questions there
As far as I know they had harsh clashes with the Native tribes, and they didn't have the firepower that the conquistadors did, so it wasn't really worthy, besides there the land was practically bald
Bibliography: https://www.youtube.com/watch?v=HgGRsBOj-y8