There were many. Timber, Silver, Gold, Iron ore, coke, steel (these last 3 actually go together and the last one is derived from iron ore), the raw materials for a chemical industry, wheat (barley oats, cattle, livestock these last I consider natural resources. Your teacher may not), grass lands (for ranches). That ought to get you started.
Because of the discovery of gold in San Francisco in 1848, many people began moving west to search for wealth and fame. The United States was discovering many things underground...gold, silver, and oil. These were some of the natural resources the United States had at the end of the 1800s.
