Agree JV! This appears to be a fine example of a better than average, original percussion Spanish trabuco. These are not seen too often, and make a nice addition to collections, especially here in the Southwest. As you pointed out, the use of gold makes this a more high end gun. Carved stock and engraving complete the ornamentation. These bring good money out here, but the flintlock seems to be more desirable where I live.
One of the Spanish explorers, around 1770, lost his gun up in Orange County and even though searching dilligently, they failed to recover it. The site is known today as Trabuco Canyon. Likely that some Juaneno Indian found it and kept it.
Dick