Humic acid products come from a wide variety of sources. The richest products come from ancient deposits that formed when plants and animals died in wetland environments. Over time, these massive beds of decaying material were covered by sand and rock formations, and they were compressed into even richer deposits.
Some deposits were then uplifted, and oxygen was reintroduced to the material, which significantly aids the formation of humic acids. These uplifted deposits are mined near the surface, and are often referred to as "lignite" or "leonardite". This is where most humic acid products come from today.