While some may say to contact your local government agency the problem is there is no one agency that oversees native sites. You do have federal laws that protect native sites NAGPRA

Federal law has provided for the repatriation and disposition of certain Native American human remains, funerary objects, sacred objects, and objects of cultural patrimony

However, that is a law and not a reporting agency. The optimal way would be to know what federal agency the land entailed belongs too. Good luck. At least in the West this is a mess. Also, especially during Covid, I wouldn't hold your breath getting them to

1 - return a call or email

2 - Do much

Answer - Your Local Colleges Anthropology Dept. The local college Anthro Dept. will likely know if it is already known or possibly a new find. There are numerous known sites throughout the Western US and these site just haven't been "worked." It takes money, time, and the rest to carefully excavate and preserve a site. These college dept also understand NAGPRA and it's implications.

If a local college doesn't respond, send an email to the largest college in your state (anthro dept) and CC the https://www.americananthro.org/

Best of luck!

Archaeologist here. For your first question about people being ousted from their ancestor's land-- I'm guessing you mean by the government, were authorities to realize it's an archaeological site? It's very unlikely. Is the land private land? If so, generally the law is that no one is going to be able to oust people from it just because it has an archaeological site on it. In the United States, unlike most other places, private landowners can do what they want on their own land, including destroy archaeological sites. NAGPRA, the main legal statute regarding the removal of Native American cultural artifacts, doesn't really prevent private landowners from doing what they want, except it does come into effect if people try to sell the objects taken. There may be certain exceptions, like if the land is physically within a reservation, or other things that I am unaware of. What I would do is look up the state and local laws.

As for preventing people from looting artifacts-- this is more tricky. You're going to run up against a lot of backlash if you start telling people they shouldn't go collect arrowheads. Most people don't understand why this is harmful to an archaeological site, and they have fond memories doing it as a kid with their own parents and grandparents. It's almost a national past time in parts of the rural US.

Can you clarify a little more about the owners of the land? Are they Native Americans themselves? Are they the ones doing the looting? I would say the first step to preventing further damage to the site is to talk to the landowner and see what their thoughts are on the matter.

Then, you could also email a professor of archaeology at a local university. You'll most likely find these people within the anthropology department. Explain the situation and ask if there's any way for the site to be surveyed and recorded. Try to ask a professor emeritus, who might be more willing to help you out as a side project in their retirement. Definitely don't email an assistant professor, since they're trying to get tenure and they won't have time.

The reality is that likely nothing will happen. Hundreds of thousands of small, ephemeral archaeological sites exist all over the US, mostly unrecorded, because there simply isn't the will or resources to document them.