In 2014, Del Kuhn said he entered this Big Bear Race in 1948 and had not seen this footage before.
He identified the motorcycle rider who is signing a clipboard at a check point as Dutch Sterner who was the winner than year.

Kuhn also identified himself as the rider following another rider without a helmet as they come into a slow curve.
The 3 Point Motorcycle Club sponsored this race. This was the new WWII veteran, Kuhn’s 2nd Big Bear race, came in 16th in 1947 and in 1948 on a HD,

Did not finish but he doesn’t remember why. Kuhn went on the win the 1952 Big Bear. GrandfathersofMotocross.com