I apologize if this has been asked before. If anyone has a link to a previous discussion about this, please drop it here and send me on my way.

I'm reading Roxanne Dunbar-Ortiz's An Indigenous Peoples' History of the United States. The author makes repeated reference to the oral histories of various North American First Nations (I apologize if that terminology is incorrect; I'm just trying to avoid the term "Indians"). I understand that these are important to the various nations because this is how lore and knowledge is traditionally passed down, but how reliable are they, from a historiographical standpoint? Do they carry the same weight for academics and researchers that written primary sources would? If so, how are they verified?

ETA that I'm not belittling or discounting oral histories in any way. I've seen numerous stories about how oral histories have confirmed events that have been found in the geologic record, such as earthquakes and tsunamis in the Pacific Northwest, or as someone mentioned in a (now-deleted?) comment, the wreck of HMS Terror was finally located thanks to oral histories of the Inuit. I even read somewhere that they're being used to devise better forest management techniques, so we can more effectively combat forest fires. Oral histories have a lot of merit.

My question has to do with their use as references in historical research. Are they given the same weight as written sources? Or do they need to be corroborated by written sources before they can be used as a viable research reference?