Fossil is a small city in north-central Oregon, named by it’s first postmaster and mayor, Thomas Hoover, after he found fossils in the clay-like rock on his ranch. The city boasts the only public fossil dig in the U.S. Access is available to anyone for a small fee of $5 and up to 3 fossils can be removed from the site. Tours and workshops are also available from the non-profit organization Oregon Paleolands Institute.
The post office, established in 1876, maintains a precancel device and several types have been used through the years. Those I’ve been able to find follow:
Type 1 has upper and lower case serif lettering and a three letter state abbreviation.
Type 1
Type 2 has upper case serif lettering and a four letter state abbreviation.
Type 2 on small format stamp
Type 2 on large format stamp
Type 3 has upper case san-serif lettering and a four letter state abbreviation.
Type 3
Type 4 has upper case san-serif lettering (thinner) and a two letter state abbreviation.
Type 4
The pre-cancels can be found in a vertical position.
Type 4 – vertical
And a bit more oddly on a large format commemorative issue that allows the precancel to show twice.
Type 4 vertically double
If you know of others, please comment and send an image. 
The Mesozoic Times 