Final answer:
The plant manager's salary at Riverland Shoes and Boots Inc. is considered a fixed cost, specifically a facility-level cost, as it does not vary with the level of production output.
Step-by-step explanation:
The plant manager's salary at Riverland Shoes and Boots Inc. would typically be classified as a fixed cost within the cost hierarchy. Fixed costs are those that do not vary with the volume of production; they are incurred regardless of how many units of product a company makes. The plant manager's salary does not change with the number of steel-toed workboots produced, making it a fixed cost, more specifically, it is an example of a facility-level cost which is associated with the costs of running the production facility as a whole.