Between one-fifth and one-third of all workers in which of the following enterprises in the West were African American, Indian, or Mexican? Mining Railroad Cattle Farming

African Americans, Native Americans, Asians, and Mexicans made up a significant proportion of all workers and settlers in the Old West during the nineteenth century. Chinese Americans in particular were known for their work on the railroads in the Old West, mainly during the 1860s. In terms of Mexicans in the Old West, it must be remembered that rather than Mexicans coming to the United States, the West expanded into what had previously been Mexico, so the Mexican population of what became Texas, in particular, was extremely high.
This question, however, probably wants you to think about the African American cattle-driving population, which was extremely significant and widely forgotten. It is actually estimated that about one quarter of all cowboys in the Old West were African American. This was a result of the Emancipation Proclamation during the Civil War, after which many blacks headed to the West in search of empty land where they could settle, build houses, and cultivate cattle. African Americans also contributed to the mining operations that formed part of the gold rush, seeking the American Dream.
You can find out more about African Americans and other nonwhite populations in the Old West in the articles linked below.
http://www.scholastic.com/browse/article.jsp?id=4807

https://www.smithsonianmag.com/history/lesser-known-history-african-american-cowboys-180962144/