A state highway to be known as state route number 501 is established as follows:
Beginning at a junction with state route number 5 at Vancouver, thence northerly by way of Lower River Road and an extension thereof to Ridgefield. State route number 501 from the northerly junction of N.W. Lower River Road to the Ridgefield city limits is designated "the Erwin O. Rieger Memorial Highway." The department may enter into an agreement with the Port of Vancouver, Clark county, or the United States Army Engineers, or any combination thereof, to obtain material dredged from the Columbia river and have it stockpiled at no expense to the state.