U-Shaped Constructions

Into this category we place those constructions which can be described as U-, C- or horseshoe-shaped.  D-shaped constructions are essentially the same, with the addition of a straight side across the two forks.  These can be of stone or earth and also include U-shaped cairns.  Herradura is the Spanish word for horseshoe, and this term is used for the low shrines found in the Anasazi region of the Southwest.  These are frequently located on high spots with good visibility of the sky.  Pueblo Bonito, at Chaco Canyon in New Mexico, is the largest of the D-shaped stoneworks in North America.     It was originally 5 stories tall with up to 800 rooms.  Semicircular stone circles with an opening (i.e., which do not fully enclose an area) are also included in this category.

New England U-shaped constructions:

Montana- "semicircular in form, and are built of selected square stones, piled up in a parapet or breastwork about four feet in height." 

New Mexico- C-shaped and D-shaped constructions at Chaco Canyon:

Indiana- C-shaped earthen mound: 

Louisiana- The massive 3800-year-old Poverty Point earthworks complex is C-shaped:

Ohio- "two horseshoe-shaped platforms that formerly laid at the northern terminus of two parallel earthen walls which ran southeasterly to the Ohio River and which continued on the Kentucky side of the river, where they led to two concentric circular enclosures."

Southwest- "Herraduras are circular to horseshoe-shaped enclosures that usually measure 5-7 m across. The low masonry walls are normally open on one side, and the majority of examples are oriented towards the east. These structures almost always open onto the surface of Chaco roads, and they tend to be situated at topographic breaks" 

Yurok Prayer Seat from the Pacific Northwest