Did the westward expansion of the US halt at the Rocky Mountains?

No, the westward expansion of the United States did not halt at the Rocky Mountains. While the Rockies presented significant geographic challenges, expansion continued beyond them, particularly during the 19th century with events like the California Gold Rush and the completion of the Transcontinental Railroad. These developments facilitated further settlement and exploration into the Pacific Northwest and beyond. Ultimately, the U.S. extended its territory all the way to the Pacific Ocean.