A single arm support apparatus for a rockwheel for excavating a trench through difficult materials, including rock. The rock cutting attachment includes a frame assembly which supports a cutting wheel in a manner that permits it to be inserted into the ground to approximately the radius of the wheel. The cutting wheel mounts to a shaft that is supported by bearings on a single side of the wheel, and is rotationally driven by a hydraulic motor. Additional structure mounted on the frame provides depth control.