My grandfather, Lyle L. Carringer (1891-1976) joined the United States Marines Corps Reserve on 7 May 1917, and served for two years on active Reserve duty and two years on inactive Reserve duty.
I found these Marines Muster Rolls online in the U.S. Marine Corps Muster Rolls, 1798-1940 collection on Ancestry.com. This one is dated May 1919, and it transfers Private Lyle L. Carringer from Active to Inactive duty:
The entry for Lyle says:
* Enlisted: 7 May 1917
* Remarks: 1-28: SD P.X. Clerk. 29 trans to inactive status as Pvt (Prov) MCR cl 4 district #16 Los Angeles Cal. Auth. MGC #66680-150EE , 2-12-19. [note: some of the letters are difficult to decipher]
Here is the entry for May 1921, which shows that Private Lyle L. Carringer enrollment in the Marine Corps Reserves has expired: