These plates are used on off-road recreational vehicles.
I believe this type started in the 1970s with motorcycle-sized blue on white plates and an A prefix, working their way through B, etc.
All-Terrain new dealer plates are also issued, with in an X1 123 format.
Click the photo to see this type in use.
See Also: Dealer All-Terrain
1985
1988
1990
1999
2000
2001
You can get a sense of how few of these were issued every year by comparing the numbers of the 2000 plate vs. the 2001
2004
When the graphic base was started, “All-Terrain” lost its hyphen and became “All Terrain”. These plates began with the “G” series.
Another 2004
Numbering in the G- series continued on to four digits.
ca. 2010s
2011
It looks like the dot disappeared later in the G- series.