Final answer:
The Atchison-Topeka and Santa Fe Railroad reached New Mexico in the 1870s, connecting Kansas City and the Missouri River Valley to the Southwest.
Step-by-step explanation:
The Atchison-Topeka and Santa Fe Railroad reached New Mexico in the 1870s. The line connected Kansas City and the Missouri River Valley to the Southwest. It played a significant role in the expansion of rail networks throughout the United States, linking different regions and facilitating faster travel.