The Colorado Street Bridge, originally constructed as a municipal highway bridge carrying one city street across another, is a skewed, single-span, masonry arch structure that has been closed to vehicular traffic and converted into a pedestrian walkway over a park meadow in the Torre de San Miguel housing development in St. Paul, Minnesota. Although the site has been extensively altered, the bridge retains integrity.
The Colorado Street Bridge is of unorthodox construction. In masonry arch bridges, the voussoirs customarily are laid in courses perpendicular to the longitudinal axis of the arch so that each course forms a continuous ring front abutment to abutment. In the Colorado Street Bridge, only the voussoirs on the face of the arch are laid in the traditional manner. All other voussoirs are laid in courses parallel to the longitudinal axis. Since the intradosal surface of the arch is sheathed in red brick, the unusual construction is concealed from view, except for a few places where the brick has fallen from place. These "holes" in the soffit also reveal that the voussoirs are both brick and limestone, alternating every two courses. The brick matches the soffit. The limestone is grey, locally quarried, rubble stone. The nature of the construction indicates that the arch is sustained by the adhesive power of the mortar rather than by the "pressure" fit of the voussoirs.
The bridge displays a variety of building stone. Red granite is used for the abutments, buff-colored limestone for the ring stones, spandrel walls, railings and coping, and local grey limestone for the curved wing walls that buttress all corners except the southeast. The wing walls are dry rubble masonry, while the railings are dressed coursed ashlar. Otherwise, the elevations display rock-faced, coursed-ashlar stonework. Joints are about one-half inch in the spandrel walls and one-quarter inch between the ring stones, which are ornamented with tooled margins. Although the face voussoirs are cut to simulate the appearance of a segmental arch, the bridge is a skewed structure. Springing approximately 5 feet above grade, the arch rises 11 feet over an oblique span of 70 feet, 6 inches. It is 58 feet in width. A heavy stringcourse marks the roadway level. The roadway itself is bordered by stone railings about 3 feet high and 2 feet thick. At the southwest corner, the railing has been removed. On both elevations, the railings noticeably dip at midpoint, indicating settlement of the arch, which partly occurred immediately after constructions
In 1927, the bridge was waterproofed by excavating the roadway and sidewalks, removing the dirt fill and sealing the crown of the arch with concrete and tar felt membrane. Repaved with a new roadway and sidewalks, the bridge remained a public highway facility until the early 1970s, when it was included in a parcel of land scheduled for redevelopment as a residential complex. Apart from replacing the roadway and sidewalks with a single sheet of blacktop, the redevelopment project had little structural impact on the bridge, although it considerably altered the general site. The most drastic change concerned the road passing under the bridge, which was vacated, excavated and landscaped as a park meadow. The bridge itself still serves a transportation function as a pedestrian walkway, linking the new housing development on the east with South Wabasha Street on the west.