On May 26, 2017, about 1445 Pacific daylight time, a Johnson Glastar airplane, N4579J, experienced a total loss of engine power while in the traffic pattern for Buchanan Field Airport (CCR), Concord, California. The student pilot, sole occupant, sustained minor injuries, and the airplane sustained substantial damage to both wings. The airplane was registered to, and operated by, the pilot as a 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed and no flight plan was filed for the local flight. The flight originated from CCR about 1443. The pilot reported that the purpose of the flight was to practice landings. The pilot took off uneventfully and flew the traffic pattern. When on the base leg, the engine suddenly quit without warning or any abnormal noises. He attempted to restart the engine several times, but to no avail. The pilot initiated a forced landing onto a roadway; during landing, the airplane's left wing impacted a light pole. The airplane traversed across an intersection when the nosewheel collapsed and the airplane slid to a rest. During a postaccident engine examination, the spark plugs were removed and exhibited normal operating signatures when compared to the Champion "check-a-plug" chart. The engine was boroscoped and no internal abnormalities were noted. The engine was rotated by hand and continuity was established all the way through to the accessory section. Thumb compression was established on all cylinders, and the valves moved freely and evenly. The magnetos were operationally tested and both produced spark. Air was blown through the fuel lines and they were clear of debris. The carburetor was fracture separated at the attachment flange and the air box sustained heavy damage. The carburetor was removed and disassembled; the fuel screen was clear of debris, and the carburetor bowl was empty. It was noted that the needle valve and floats were stuck in the up position. Slight force was applied to the float assembly and it moved freely; there were no contaminates or obvious bends in the float system.