The crossing of the St. Croix River was difficult for the railway, since the original bridge across the river was very low and trains had to contend with steep grades on both sides of the river. This made it necessary to use helper engines and to make trains shorter.
The old bridge mentioned here is the Wisconsin Central Bridge Ruins. The Arcola High Bridge (aka Soo Line High Bridge) was build upstream.
Wisconsin Central Bridge Ruins, Somerset, WI (johnweeks.com)The Wisconsin Central bridge over the Saint Croix river was built in 1884 by the Union Bridge & Iron Works. The Wisconsin Central was pushing west, and this bridge was the last link to connect Milwaukee and Chicago to Saint Paul. The bridge features a number of very well crafted cut-stone piers. There were nine 160-foot deck truss spans, one 160-foot pin-connected though truss span, and 25 plate girder spans, each 30-feet long.