Re:
I think that the compelling line of thought that I am developing from this thread is that the "Mountain Bike" was a bicycle design that came out of California and went 'viral' worldwide.
Once the "Mountain Bike" design spread worldwide it ceased to be the property of its original contributors and evolved and diversified to produce many different designs. As a result modern mountain bikes owe only a small proportion of their 'genes' to the original Californian "Mountain Bike. Hence the difficulty in defining exactly what a modern mountain bike is.
The original "Mountain Bike" was not an invention as none of its features were new or novel in themselves.
Nor did it have an inventor but a number of people, influences and ideas that all contributed to the design over many years. Not all of which originated in America.
Some of these contributors were more important to the original "Mountain Bike's" success than others and some where pivotal, in that if they had not been involved the design may have, not developed as it did, or proved so successful.
As for mentioning Geoff Apps, according to Joe Breeze, Apps and his sending large diameter Hakkapeliitta tyres to Marin was pivotal in the seeding of the idea that eventually led to the development of the larger wheel mountain bikes.