geography
what explorer first visited the u. s. river, which is the largest within its state, creating a natural boundary with mexico?

Juan de Onate was the explorer who first visited the US river, the river is the Rio Grande. In 1598 he crossed the Rio Grande in El Paso. From there he sent out small parties in all directions to search for treasure that did not exist

Explanation:

Since 1848, the Rio Grande has marked the boundary between Mexico and the United States from the twin cities of El Paso, Texas, and Ciudad Juárez, Chihuahua, to the Gulf of Mexico.

answer biscay bay;