FamilySearch has digitized an Index of Cassia County Marriages BUT it is non-searchable AND it is lumped in with the land records (making it very difficult to find!)
The Index is under:
Idaho, Cassia County Records, 1879-1960
Land and property records
Marriages, Deeds, Water Claims and Brands, vol. 1
Here's a link:https://familysearch.org/pal:/MM9.3.1/TH-1942-21939-10399-24...
You can browse the records chronologically.
Just thought I'd share....