This is another step in the process of rug weaving for the Navajo crafters. Carding is the process of separating the long fiber wool from the short, along with any debris that may remain in the wool after shearing. Hand carding is much less common now.
The caption on the front states: Carding wool to be used in Navajo Indian rug weaving, Gallup, New Mexico.
This postcard likely dates from the 1940s.