https://pentonusa.org/forum/topic.asp?TOPIC_ID=19598
Steve Minor just posted a couple weeks ago a video of a 1960's Scottish MX that demonstrates "old fashioned natural track". We had one of those in Ohio, 1968:
https://www.youtube.com/watch?v=tvuwGeVpP5w
Earlier POG posts about it:
https://pentonusa.org/forum/topic.asp?TOPIC_ID=13221&SearchTerms=inter-am
https://pentonusa.org/forum/topic.asp?TOPIC_ID=15987&SearchTerms=inter-am
https://pentonusa.org/forum/topic.asp?TOPIC_ID=18511&SearchTerms=inter-am
Tom Penton