We report measurements of the profile of the wakefieldinduced energy loss of the beam along the 1.2 km long SLC North Collider Arc. By measuring orbit differences in dispersive regions for different bunch lengths, the wakefieldgenerated energy loss is distinguished from losses due to synchrotron radiation. Calculations of the wakefields arising in the arc chambers are given and used in simulations of the evolution of the longitudinal phase space along the arcs. The measurements are consistent with the calculations. By this method wakefield anomalies in the arcs can be found. In addition, with a non-standard setting of parameters the bunch can be compressed down to 50 m, and the wakefield effect of an ultra-short bunch can be observed. Results for the final focus wakefield-induced losses are also given.