The date of the photo was during the Aisne-Marne Offensive.
The 1st Division was in a secondary attack from the east (south of Soissons) and advanced about 10 miles in three weeks.
Once the Germans were out of their trenches and retreating the ground would not present the classic Western Front trenches and barbed wire landscape. The ground the gun and doughboys are on could very well have been a German position, just not highly developed.
And of course, his object was to depict US soldiers, not to record the landscape for posterity.
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