Designed in a simple Mission style, the Winston E. Arnow U.S. Courthouse has a full, partially exposed basement, with three full stories above the basement, plus a fourth level mechanical penthouse.
The first through third levels of the front portion of the building (the west elevation and the two west-most bays of the north and south elevations) are faced with Oolitic limestone resting on a concrete base. Recessed window planes are smooth stucco. Three bands of limestone moldings circle this portion of the building, once at the watertable, with two belt courses between the second and third floor windows. A stone screen hides small first floor windows on the north and south elevations. On the rear portion of the building the walls are stuccoed within a single plane. Flat limestone bands repeat the watertable and beltcourses of the front portion, as well as continuing the eaves line of the roof over the front portion of the building. The parapet wall of the rear portion is also topped by a limestone bed molding, just below the coping. A red clay Mission tile hipped roof covers the front portion of the building, while a flat foam roof covers the rear portion. The mechanical penthouse repeats the stucco walls, stone bed molding, and both tiled, hipped roof and foam covered, flat roof. A shallow balcony, with a handsome wrought-iron railing runs nearly the entire width of the front elevation. Even more elaborate wrought-iron grilles cover the transoms over the main entry doors. Equally handsome wrought-iron fixtures flank the main west entries and the south entry to the basement.
Inside, a variety of marbles, polished bronze, colorful terrazzo, and plaster and wood moldings are just some of the original materials used to finish the spaces. The main public spaces, such as the public lobby and original courtroom and its lobby, retain much of their original character with marble or wood wainscoting, molded plaster cornices, columns and other moldings, molded wood door trim and paneled wood doors, marble stairs with bronze handrails, and patterned asphalt tile or terrazzo floors.