This is a modified carriage with pneumatic tires (post WW1). The US 155C US are heteroclit equipments that can be 100% made in France, 100% made in US, or anything in between (probably the case in here).
A second 155C has been sent back to USA...
Breech markings : '155C Mle 1911 - Schneider - Tarbes 1920 - 5599'. Carriage : 'N° 677 - CARR.HOW.155MA1 - M1918A3 - ROCKISLAND ARSENAL - 1941'
The Uxegney and Bois l'Abbé forts can be visited : fort-uxegney@wanadoo.fr