Final answer:
The La Salle expedition provoked Spanish concern over French interest in Texas, leading to Spanish reinforcement of the region through missions, presidios, and settlements.
Step-by-step explanation:
The significance of the La Salle expedition to the Spanish was that it sparked Spanish fears for potential French interest in Texas. This is because the expedition showed that France was eyeing the area that is now known as Texas, an area that was under Spanish claim. The Spanish response was the establishment of missions, military outposts called presidios, and towns to protect their claim from being threatened by the French presence. This stabilization of Spanish presence in the region became part of what defined the Spanish Colonial era in the late 1690s.