Maclay's Mill, Twin Bridge (East) is a three-span, camelback, closed-spandrei stone arch bridge. Constructed of semi-coursed local limestone rubble and blocks, the bridge is 173'-7" long and an average of 20'-9" wide with a single i6'-4" travel lane. The bridge spans Conodoguinet Creek on a perpendicular alignment and rests on two 6'-0"-wide conical piers. Its approaches have abutments with wing wails that expand to widths of 26'-0" on the west and 25'-0" on the east.
The stone with which the bridge is constructed is a weathered Cambro-Ordovician limestone, a fossiliferous dark blue-black limestone that weathers to a lighter tan color.' Its three segmental arches have spans, measured from east to west, of 29'-l", 32'-7-l/2", and 28-10-1/2". The arches rise, again from east to west, 6'-10", 8'-0-l/2", and 6'-2-3/4". There is a rectangular marble date stone set into the bridge's north parapet at mid-span. The inscription reads: "BUILT BY SILAS HARRY / 1827 / COMMISSIONERS / BENJAMIN KEYSER / WILLIAM REYNOLDS / WILLIAM HEYSER / To Roxberry 4 Miles / to Shippensburg 4 Miles." There are directional arrows pointing toward Shippensburg and Roxbury.
The bridge's three segmental arches are defined by dressed squared voussoirs and dressed springers. Keystones in each arch ring are not accentuated. Each arch ring was constructed with regular coursed ashlar blocks. The intrados of each arch barrel has been clad in cement. The masonry joints have been repointed with a hai*d cement mortar throughout much of the structure in a raised, irregular pattern. The bridge's parapets have a single 2"-thick limestone coping course that is clad in cement. The north parapet has a low elevation above the road bed: measured at the west end, mid-span, and east end (the west end being datum), it rises 4'-5", 6'-4", and 2'-6".