This is a link to a photo from the Kansas State Historical Society:
It shows workmen engaged in some activity along a string of boxcars and racks of lumber spaced out along the cars. The caption notes that this is conditioning yard at Clovis, New Mexico.
My initial thoughts are that the cars are being prepared for grain doors or that car interiors are being refurbished. The lack of used, broken boards on the ground probably weights against refurbishing.
Can anyone make an educated guess as to what actually is the activity?