I think its funny reading though this thread and seeing people deny the Spaniards being in Colorado. When Zebulon Pike made his expedition to explore the west, at the behest of Thomas Jefferson, he was met by Spanish soldiers to make sure he didn't pass into their territory, which would later be the Louisiana purchase. He was met at the Arkansas river somewhere around where Lamar Colorado is today.
I have also visited the old Spanish mission along the Purgatory river near La Junta, CO. The river is named for a Spanish expedition that went up the river and never returned.
Nothing remarkable about that. Those Spanish soldiers were from northern New Mexico, a Spanish stronghold since 1598. Santa Fe became their capital in 1610, from which they poked all around in the region since. Pike's people were jailed when caught snooping.
Of course there was Spanish prospecting and a few successful mining Spanish forays into CO, UT, AZ, CA and NM before Mexican Independence in 1821. A very few sites in UT, AZ and NM from the Spanish period remain unconfirmed and intriguing. IMO, with some exceptions, the old discoveries exploited by Mexicans and Anglos up to about WWII are known and economically played out. The allegation that there are numerous Spanish 'King's Fifth' caches all over the place is pure balderdash. If you are a cache hunter, concentrate on old fence lines and the like near abandoned structures. Although most post-hole banks have already been retrieved, your chances are still better.