Similar kinds of unifacial specimens were found on old terraces above active cobble washes and arroyos in and around San Diego by Richard Cerruti (San Diego Museum of Natural History), the same individual who showed me how they could have been made, and who also collects varieties of naturally modified specimens.
Each of the possible unifaces exhibits a couple of the same features seen on the experimental specimens, including jutting unifacial edges and proximal bulb complexes. The unifacial "artifacts" shown here are admittedly ambiguous (at least for New World eyes) which is the reason they were chosen. It is clear why they generally go unrecognized among local archaeologists. Had I not seen the reduction phenomena myself, I probably wouldn't have looked twice at them. Now I am not so sure. Under certain circumstances, they could have been fractured through natural agencies associated with cobble washes that mimic the operation demonstrated above section on proximal unifaces. The question remains: were they? If so, the fractures occurred prior to or during the formation of the terraces.
A number of other items turn up on or in these old terraces, many typical of direct percussion forms, notably discoidal bifaces (or bifacial discoids if you prefer; I am hesitant to use the term "ovate biface" at this point). These are percussion forms known throughout the world, with various versions of them turning up in any quarry where folks knew about bifacial reduction. These are a bit more difficult to pin on Nature's handiwork, but they continue to be overlooked as well. All are shown with a copy that roughly defines the bifacial facets of probable flake scars.
If these actually are artifacts, how do we know how old they are?
No way to tell, at this point. Occurring on the surfaces of terraces above the creek beds and washes, it is very difficult to assign these pieces temporally. They could be Late Paleo to Archaic. They could be older. For the moment, this is a secondary consideration. Before we can assign them to an age, they need to be identified. An improved set of criteria for discerning artifact from geo-fact may be needed. A slight knowledge of bipolar variability may help us to recognize that need.