To provide for the river navigation, the U. S. Engineers required a minimum horizontal clearance normal to the channel of 120 feet and a vertical clearance of at least sixty-six feet above low water, in case a high level type of bridge were adopted. After careful study it was decided to construct a high level bridge of the deck type, and to carry the pony channel span on cantilevers projecting from the adjoining spans, giving an arch effect over the channel. By this type of construction, a clear distance of about 145 feet between channel piers was obtained. To minimize the cost of fabrication and erection of steel, four spans were made practically the same. The east span was necessarily shorter than the typical ones, since otherwise it would place the channel opening too far across the river. This span is not so deep as the adjoining one, and the difference in height is made up by means of a rocker under the small span, which, of course, also serves the purpose of movable shoes. The channel span rests on cast steel rockers on one end, which are carried by a shelf on the cantilever panel. The opposite end of the span was pin connected. Previous to the design of the bridge, wash borings were made, which indicated in a general way that the bed of the stream was composed of a few feet of gravel, underlaid with sand for a considerable depth. It was accordingly decided to carry the foundations down below the probable point of future scour, and carry the loads entirely upon piling. The two channel piers were sunk about thirty-five feet below low water. The west approach is carried on fir piling treated in an open vat with carbolineum to a temperature of about 220 degrees F. Lumber being comparatively cheap, the entire roadway deck of the bridge and wooden approach is composed of fir, three by seven inches and twenty-six feet long on edge, spiked together, thus projecting a foot outside the curb on either side, the roadway being twenty-four feet between curbs. An asphaltic wearing surface three and one-half inches thick effectively waterproofs the wood, and the small interstices between the pieces will allow sufficient circulation of air to preclude any possibility of attack of dry rot. The ends of the floor members were painted with hot carbolineum, as were also the wooden members contiguous to openings in the floor occasioned by expansion joints between spans.