The spanish were encouraged in their exploration of the area north of mexico because

The Spaniards, in search of riches and new lands to conquer, together with the ancient legend of El Dorado, the land rich in gold and in abundance of all kinds, led them to explore, map and conquer northern Mexico, whose most famous explorers were Albar Nuñez Cabeza de Vaca and Alonso Álvarez de Pineda, who explored all of northern Mexico and even reached the territories of Texas and California, in their search for villages full of gold, and lands that had the same abundance of resources that the center and south of Mexico had.