@John Alaska: What you seem to want looks rather redundant, and would be akin to using the Caption field metadata as a generic tagging field, whereas the Caption field is usually for data that is peculiar to a particular image. The Keywords (Tag) field would seem to be more appropriate for what you need.
Some people might use a mass file rename to cater for this, so the identifying text would then be in the filename, but that just clutters up the filename with metadata.
However, if you were a Google Picasa user (as I am) then, you would probably select all the image files you wanted to cover with the chosen specific term and attach it as a Tag "Grand Canyon North Rim". You could later create a virtual album for that Tag name and put it up in the image store (Cloud) with that as the album name, and share it as you wanted. You can attach multiple, different tags to a given image file.
Picasa Tags are included in (attached as) Keyword field file metadata, and so stay with the file. Other image managers would thus be able to pick up that metadata. One needs to be aware though that due to the apparently somewhat loose implementation of standards for image file metadata in image management tools, some metadata might come under a different category of metadata depending on what image management tool you use.
Thus, my recommendation would be try to maintain some degree of consistency and only use a single image management tool - e.g., (say) such as Picasa or some other decent image management tool - and drop the idea of effectively trying to use the "Caption" metadata as a generic tagging field. Instead, use the provided Tagging functionality for tagging.
