Hi Ruth:
They were divorced in Umatilla County:

Case# 140-038
Name Lowery, Annie J vs Lowery, Walter A
Date
Record Type Divorce
County Umatilla
Source County

You can try contacting the courthouse:
Courthouse
216 SE 4th
Pendleton, OR 97801
County Records: (541) 278-6236

Or check out the State Archives:
Oregon State Archives
800 Summer St. NE
Salem, OR 97310
Phone: 503-373-0701
Fax: 503-373-0953
reference.archives@state.or.us

Good Luck!
Laura