Nanometer-scale roughness on a solid surface has significant effects on friction, since inter-surface forces operate predominantly within a nanometer-scale gap distance in frictional contact. To study the effects of nanometer-scale roughness, two novel atomic- force-microscope (AFM) friction experiments were conducted, each utilizing a gold surface sliding against a flat mica surface as the representative friction system. In one of the experiments a pillar-shaped single nano-asperity of gold was used to measure the molecular-level frictional behavior. The adhesive friction stress was measured to be 264 MPa and the molecular friction factor 0.0108 for a direct gold-mica contact. The nano- asperity was flattened in contact, although its hardness at this lengh scale is estimated to be 3.68 GPa. It was found that such a high pressure could be reached with the help of condensed-water capillary forces. In the second experiment, a micrometer-scale asperity with nanometer-scale roughness exhibited a single-asperity-like response of friction. However, the apparent frictional stress, 40.5 MPa, fell well below the Hurtado-Kim model prediction of 208-245 MPa. In addition, the multiple nano-asperities were flattened during the frictional process, exhibiting load- and slip-history dependent frictional behavior.