A more thorough explanation:

A mill site is a small piece of land that is located near a watercourse and is suitable for building and operating a mill. It can also refer to a small parcel of nonmineral public land, not exceeding five acres, that is claimed and occupied by an owner of a mining claim because the extra space is needed for mining or ore-reduction operations.

• A farmer owns a small piece of land near a river that has a strong current. He decides to build a mill on the land to grind his wheat into flour. This land is considered a mill site.
• A mining company owns a mining claim that is located on a small piece of land. They need extra space to store their equipment and process the ore they extract. They claim and occupy a nearby piece of nonmineral public land, not exceeding five acres, which is considered a mill site.

These examples illustrate how a mill site can be used for different purposes, such as milling wheat or processing ore. It is a small piece of land that is located near a watercourse and is suitable for building and operating a mill.