It seems like most of the major battles from 1915 onwards occurred from around Verdun north. That leads me to, naively, kind of mentally picture a bunch of Germans and Frenchmen hanging around in their respective trenches near Mulhouse smoking and griping about the weather and not fighting very much.
What was happening in the southern half of the front (The Vosges Mountains, Alsace etc.) from 1915 through 1918? Were they in a state of stalemate (like they seem to be when you read a summary of the war)? What kind of troops held the line - was it held by reservists, did they have fewer artillery pieces and machine guns, etc?
There was some intermittent fighting on the frontline that stretched through the Argonne and the Vosges to the Swiss Frontier, notably in the Argonne Forest itself (Rommel describes the fighting here in Infantry Attacks) and around the hilltop known as Hartmannwillerskopf, but it was mostly quiet here by 1916. Army Detachments A & B (?) were the German HQs in charge of the line here, with Castelnau being in charge of the French Army Group opposite them. Positions were thinly held, to free up man power for elsewhere, but in 1918 the AEF launched the Meuse-Argonne Offensive here, and drove the Germans back, albeit at high cost.