I suspect there are many similar reserves around the world. These are as yet unexplored or incompletely explored because they were not considered recoverable until recently. The US may not be a bit exceptional, other than in having had more applicable exploration done - so far. This will certainly change and great new finds will become commonplace. If so, natural gas and petroleum will be local local resources, more similar to hydro or coal, and not global concerns.
Good observation.
Oil shale is likely found all over.