However according to Charlie Kelly, Charlie Cunningham did use a 700x38C front wheel one of his personal bike as early as 1978.
Here is a quote regarding Charlie Cunningham's bike from Mark Slate of WTB. (Mark was involved in the creation of the 700x52C NanoRaptor that is now commonly referred to as the first true 29er tyre).
"Charlie has been riding a 700x35c tire bike since I think about 1978. I think the first thing Charlie heard of a fat tire for 700c rims was when Wes came out here and brought his "Mountie" with 700x47c Goliath tires." (Though it is not impossible that Charlie knew of the 700x47c Hakkapeliittas that Geoff Apps offered to export in 1980).
So it would seem that Charlie Cunningham may have also had some influence on the thoughts that a 700c mountain bike wheel may be viable thing.
The bike(s) being referred to by Kelly and Slate were not at all what most people -- including Cunningham himself -- would think of as “mountain bikes”. Rather, they were adaptations of road or cyclocross-style bikes. This model, distinct from Cunningham's mountain bikes, was referred to variously as the “Cyclocross/Multi Purpose” or “Expedition” bike in the Cunningham InfoPacs:
This is a rugged skinny tire bike which is built for tires up to 35mm or 1.375”. The bike is a light 21 lbs with Expedition tires. I have enjoyed my own M.P. bike so much that it has inspired me to build this incredibly practical and fun bike for others. My appreciation of this type of bike stems from the fact that it is very efficient on pavement, while being tough enough to go anywhere a mountain bike can go with a little rider finesse. The bike is ideal for efficient travel over varied terrains, including pavement. With lighter rims and tires it can double as an excellent road bike.
Cunningham’s first fully self-built bike -- which he would
call a “mountain bike” -- is CCPROTO from 1979. It has 26” wheels front and rear. That bike is one of the two Cunninghams on display at SFO.
The bike in the photograph with Fairfax Pat is from the early 1990’s. The frame was built for a 26” wheel suspension fork. A decade or so later when the Panaracer 700x45c FireCross tire became available, Cunningham re-purposed that bike with the new fork shown --- which would be after
all of the Williams/Gordon/NanoRaptor activity. This bike is probably more accurately seen as an extension of Cunningham’s experimenting with mixed wheel sizes rather than as an “early 29’er”.
The best source for accurate information on Cunningham and his bikes is http://www.cunninghambikes.com