Shortly after the end of the American Civil War in 1865, thousands of Americans rushed westward to develop the vast lands of the western territories. This large-scale westward expansion continued for nearly 40 years. Lands that were once vast and barren quickly became populated with settlers. The discovery of gold in California attracted many people to mining.

People flocked to the goldfields with dreams of getting rich. Although only a small number actually found gold, most worked hard and, after spending all their money, gave up the dream of striking it rich, choosing instead to stay in California as farmers, merchants, or laborers.

Some, however, did not abandon their dreams of wealth. They turned eastward, exploring the wilderness between California and the Mississippi River in search of gold and silver. Gold and silver deposits were discovered in Nevada, Idaho, and Montana, while others found gold in Arizona, Colorado, and the Dakota territories.

The first arrivals in Colorado reported back that gold was everywhere, and that with hard work, one could earn the equivalent of $5–$10 a day, sometimes even more.

However, those who rushed to the goldfields soon realized that gold was not as abundant as imagined. In the streams flowing down the mountains, it became increasingly difficult to find gold. Mining required digging into the mountains with large machinery, which was very expensive and unaffordable for most individuals.

Some miners organized themselves into companies, borrowing from eastern banks or raising capital by listing their companies on the stock market. Within a few years, most of the gold mined in Colorado came from these mining companies.

Many of those who went west for gold stayed, taking up farming or opening shops. Others continued further west, to Nevada and California, in search of more gold. Some cut timber and sold it; timber from Oregon and Washington was shipped not only to California and Mexico but even to China and Hawaii.

Every new gold rush attracted large numbers of people from the East. Mining camps quickly developed into small towns with shops, inns, and even local newspapers. However, most of these towns existed only while the gold rush was active; when gold became scarce, the towns declined.

In some gold regions, large mining companies bought up entire areas of land from the original landowners. These companies brought in machinery to mine deep underground and extract gold from ore. They required equipment and other supplies, giving rise to transportation companies that hauled supplies with oxen-drawn carts. Roads were built, and in some cases, railroads were constructed.

The wealth generated from gold and silver mines was invested in other industries, such as shipping, railroads, factories, stores, and land. This created more employment opportunities in the West and improved living conditions, encouraging more people to leave the East and start new lives in the West.

Eastern cities also continued to develop, establishing new factories and industrial centers. People left farmlands to work in cities. Industrial development increased demand for food and meat. Chicago became a center for slaughtering and meatpacking. Livestock were transported by railroad to Chicago, where meatpacking companies slaughtered, packaged, and shipped the products to eastern markets. Special refrigerated railcars kept meat fresh during transport. Rising demand for fresh meat required increasing numbers of cattle.