> [Oregon Trail] was in fact first written in 1971 by three educators at Carleton College, a small liberal arts college in Northfield, Minnesota. Don Rawitsch, Bill Heinemann — no relation to the “Burger Bill” Heineman who worked on The Bard’s Tale series among other games — and Paul Dillenberger wrote the game in BASIC on an HP-2100 series minicomputer. - http://www.filfre.net/2011/03/on-the-trail-of-the-oregon-tra...
Source code for a version from 3/27/75 at http://www.filfre.net/misc/oregon1975.bas .
See also http://en.wikipedia.org/wiki/The_Oregon_Trail_%28video_game%... for the 1971 creation date.
10 REM O R E G O N ** 1/1/76
20 REM ORIGINAL PROGRAMMING BY BILL HEINEMANN - 1971
30 REM SUPPORT AND RESEARCH MATERIAL BY DON RAWITSCH
Normally, I wouldn't know this, but just in the last week I found a copy of that version of Oregon Trail that is mentioned. I used it as part of a demo of a project I'm working on. Because I could, I whipped together a quick and dirty BASIC interpreter to actually run the code live. The copy I had received had several typographic errors, as I believe it was copied from a poorly-scanned image of a magazine article. I've changed it only insomuch as was necessary to get the game running.
In the process of working on this, I fell into the typical wikipedia-esque rabbit hole of reading links and references and everything even tangentially related. Which is great for deadlines :P
While the date in the source file OREGON.BAS says 1978, a year after ATOM 20, and it does have the same shooting mini game where you type the words "bang" and "pow", I don't think that is enough to say Oregon is based on Atom 20. Rawitsch and Heinemann had been working on the idea since 1971. They built it for a mainframe system that was specifically in use by Minnesota school districts. 1978 was when they first publicaly published the OREGON.BAS, but they had been doing extensive testing with the kids in school up to that point.
So I'm only guessing. It could be that the shooting mini game was a last minute addition to Oregon after an encounter with Atom 20. Hunting as a concept was always core to the design, but who knows if the actual "type this word" game was there. This page  seems to suggest the mini game was present even in 1971, but it doesn't explicitly say so, and I've come to learn that journalists can mess up these sorts of details. However, I wouldn't be surprised if Atom 20 were the one to receive the inspiration from an early, pre release version of Oregon, maybe even developed by one of those students or faculty in Minnesota who had played it on the mainframe system (apparently even then it was quite popular).
I'm heading to a funeral. Googling Ray Brander popped up a LinkedIn profile that seemed a likely good match. Maybe someone can contact him and find out!
EDIT: looks like Don Rawitsch has an active LinkedIn profile, too, and is open to contact.
0 REM --ATOM 20
1 REM --VERSION: 7/1/77
3 REM --AUTHOR: RAY BRANDER
4 REM -- TWO HARBORS
5 REM --CDC CYBER 70/73-26 BASIC 3.1
The CDC Cyber 70 was an early 1970s mainframe:
Note that it was developed in Two Harbors, Minnesota.