The Manito Park stone bridge is made of a stone common to the Spokane area and also a prominent building material in Manito Park itself called Basalt Stone.
Basalt comes in a variety of colors from a lighter tan to a dark rust or grey tone. It is a hard stone good for walls and bridges. Spokane residents also use Basalt stones as a landscaping feature in the yards of their homes and due to the stone's abundance in the Spokane area, it is also relatively inexpensive.
Some basalt stone is porous with small pox marks. Basalt is a volcanic stone that was cooled very rapidly. The pox marks are suspected to be from water present when the magma first hit the cold possibly snowy landscape - it then rapidly evaporated, leaving the marks.