maps

[stockastic]

I recently did a photo that include a piece of a USGS topographic map.  I chose an area without much text, and before submitting, I cloned out every bit of what text there was, leaving nothing but lines and color.  Shutterstock rejected it for copyright. However, USGS topographics ARE in the public domain:
   http://nationalmap.gov/ustopo/faq.html

Is this rejection typical, and is it the same at other agencies?

Might the image be accepted if I credited USGS in the description - like we do with NASA photos?