Oso Flaco as far as I know is a place rather then a town. It is farm land. There ia a railroad siding not far from there and maybe there was a construction camp at one time. The 1870s would have been about right for the railroad being built through the area. It is in San Luis Obispo County. Just northwest of Santa Maria and across the county line a few miles. Off of route 1 on todays maps. I first went to Oso Flaco about 60 years ago before the park was started and a fee charged, and it consisted of a dirt road that ran between two small freshwater lakes. One was not more then a pond and the other covered several acres and had duck blinds out on the lake. (they are gone now) There was a parking area for the sand dune users. Dune buggys could be seen there almost any weekend. The marriage you speak of may have been at a farm or ranch in the area. Oso Flaco is a name for the area from back in the missionary days when explorers camped in the area, while going between mission sites. It got it's name because of the bears in the area. (now also gone) Maybe someone knows more of the areas history. You might try writting the San Luis Obispo Historical Society. I belive they have a web site.