Assuming this is the bit that is attempting to change your background image:
@media screen and (max-device-width: 480px) {
#allthingsus {
background-color:#FFF;
}
You're only setting a background-color and therefore not changing the background-image. You need to set background-image: none;
for this media query.
Edit
Couldn't really test using the media query max-device-width
so have done a fiddle here (http://jsfiddle.net/rnewport/em35H/1/) using max-width
instead and it seemed to be working ok for that