Insect and Spider Identification: tons of light colored cocoons in my yard - please help ID!, 1 by elborelli

elborelli wrote:
I am new to Arizona, so I am not sure if this is a common thing to find here. In our backyard are TONS of these small (1 inch long) cocoons that look like seashells and are hard like seashells. They are not usually on the surface of the ground, but we find many of them when we dig into the soil. When they are cleaned off they are almost white, but these in the picture have dirt on them. Does anyone have any idea what these are? Thank you for your help!!