Oh, what a sweet little bit of news reportage this is!
‘This segment, hosted by Steve Fox and showcasing the founders of mountain bike racing, comes from the Paul Colardo collection in the William French Archive. Paul was one of ‘Evening’s’ cameramen and producers. Steve Kotton, cameraman on this shoot, had to testify in court over a lawsuit brought against KPIX by one of the riders. They claimed Steve was in the middle of the road on a turn, thus causing the rider to crash. The rider lost the case, since video tape does not lie and Steve was on the side (you can see it in this segment).’
Amongst the Klunkers is one Gary Fisher, of Fisher Bikes, and the visionary of the sport can be seen here muttering about this style of riding that “It’s gone a long ways and it’s going to go a long ways.”
Here’s a 1980 Klunker.

And here’s GF looking like he’s ready to bust some gnarly downhill… (I know, it just doesn’t sound right when an Englishman says ‘gnarly’, apologies!) Amazing how his look at that time would fit in right now with certain young tribes amongst us now…

And the video, enjoy!
And if you’re into this kind of thing, here’s a history of MTB from the Marin Museum of Cycling.