Scanning tunneling microscopy experiments reveal the formation of a variety of geometrically exotic nanostructures following submonolayer deposition of Ag on Ag(100). These result from the diffusion of large Ag clusters, and their subsequent “collision” and coalescence with extended step edges, and with other clusters. Relaxation of these far-from-equilibrium step-edge configurations is monitored to determine rates for restructuring versus local geometry and feature size. This behavior is analyzed with lattice-gas model simulations to elucidate the underlying atomistic mass transport processes.