After another trip to Arizona, I started pondering how Native American sites (Canada, United States, and Northern Mexico), are represented on the world heritage list. There are (8) inscribed properties that fall under my definition of "Native American". I am including ancient and more modern sites, I exclude Hawaii. My question ultimately led to, are Native American cultures under-represented on the world heritage list?

I suppose there are 2 approaches to nominating new Native American sites.

Type 1) Nominating - adobe/stone ruins, pueblos, mounds, pictographs, petroglyphs (This type of nomination includes all properties from the United States and Mexico)

Type 2) Nominating - mixed properties, cultural landscapes (often a lack of major physical structures in nomination. Canada has and is currently doing these types of nominations)

*Most if not all Native American nominations demonstrate these (2) criteria.

3. to bear a unique or at least exceptional testimony to a cultural tradition or to a civilization which is living or which has disappeared;
5. to be an outstanding example of a traditional human settlement, land-use, or sea-use which is representative of a culture (or cultures), or human interaction with the environment especially when it has become vulnerable under the impact of irreversible change

Canada
Head-Smashed-In Buffalo Jump (1981)
SGang Gwaay (1981)

United States of America
Mesa Verde National Park (1978)
Cahokia Mounds State Historic Site (1982)
Chaco Culture (1987)
Taos Pueblo (1992)

Mexico
Rock Paintings of the Sierra de San Francisco (1993)
Archaeological Zone of Paquimé, Casas Grandes (1998)

Tentative (Native American) Nominations for the United States
- Hopewell Ceremonial Earthworks and Serpent Mound (2008)
- Poverty Point State Historic Site (2008)

The United States continues nominating "Type 1" style nominations.
Canada has quite a few "Type 2" style nominations in the works.

The United States (and likely Mexico) has significant "Type 1 & 2" potential nominations. Canada lacks "Type 1" style sites primarily because of climate and traditionally wooden building materials used by the native peoples.

Example of "Type 1" potential nomination in the United States
- Sinagua Culture (Arizona)
- Hohokam Culture (Arizona)
- Canyon de Chelly National Monument (Arizona) *Mixed property
- Chumash Pictographs (California)
- Zuni Pueblo (New Mexico)
- Pipestone National Monument (Minnesota)

Example of "Type 2" potential nominations in the United States
- Great Plains Cultural Landscape (South Dakota, Nebraska)
- Trail of Tears Sites (Georgia)
- Voyager's National Park (Minnesota) *Mixed property
- Wounded Knee National Historic Landmark (South Dakota)

I would extend your argument, winterkjm, to all of the Americas. Pre-Columbian monuments are certainly underrepresented in the list and not too prevalent on the current T-lists. The other type you recognise: mixed sites and CLs are missing altogether not only in the USA but in all of the Americas apart from Canada. It is rather striking that countries with vibrant indigenous population such as Brazil, Peru, Mexico, Guatemala, Panama, Paraguay etc. never propose any sites associated with these living cultures.
I think that this originates from centuries of Colonial indoctrination that led the locals to believe that their Colonial architecture is their main tribute. I am not underestimating what the Americas has to offer in terms of Colonial architecture. I just find it so shameful that other types of sites such as CLs, Precolumbian sites, modern architecture and even natural sites are so strongly underrepresented.
An excellent example is Brazil. Out of 19 sites it has 9 are colonial and only 7 are natural. This is despite the immense size and great importance of its nature. Precolumbian sites are represented by one nomination. Modern architecture by one. Only one single CL and no single mixed site.

Brazil is rather striking.

The big 3 in Latin America - Maya, Aztec, and Inca do have varying degrees of representation. Though nowhere near Rome, Ottoman, or the Habsburgs. However, there are numerous cultures/civilizations beyond these classic eras with little to no representation on the world heritage list.