The Western White butterfly (Pontia occidentalis) looks similar to, and belongs to the same genus of white butterflies, as the Checkered White. With the exception of the far Southwest, the Western White's range extends from the Rocky Mountains to the Pacific Coast.
Females, like the one in the top picture, are characterized by a dark spotted pattern on the top and bottom wings. According to most experts, the pattern on the Western White female is typically darker than the pattern on the Checkered White female.
Comparing wing patterns on the males is often the best way to differentiate between Western Whites and Checkered Whites.
The row of black spots on the border of the top wing in the Western White male on the bottom picture is larger than the marks that border the Checkered White. The bottom wing lacks dark spots or patterns.
