In California, a few years before the state became officially part of the U.S., a large portion of gold was found in the land, and after word spreaded out about the discovery, people from many countries flocked to California seeking the riches. This event was known as the "California Gold Rush", and it allowed the state to increase its port entry tariffs for all customs, as well as booming the economy of the country overall.
The economic growth helped the population increase, and the state's infrastructure and landscape were shaped in american style with the construction of roads, farms, businesses, saloons, schools, and other assets of the sort.
The annexation of New Mexico meant the U.S. would acquire its lands rich in minerals as well. Many mines abundant in minerals such as gold, silver, zinc, lead, copper, and molybdenum contributed to the state's economy. Moreover, New Mexico greatly provides growth with livestock products - mainly dairy and cattle -, and with crops such as pecans, hay, and onions as well.