This paper reports the observation of 164 definite and 20 ambiguous examples of the reaction K-+He4-->Λ0+π- +p+d produced by K--meson absorptions at rest in the Northwestern University 20-cm liquid-helium bubble chamber. We confirm that the reaction is dominated by the two-step process K-+He4-->(Σ+nucleus)+π- -->Λ0+p+d+π-. The momentum distributions of the baryonic particles (for events with π--meson momentum below 180 MeVc are compared with the predictions of an impulse-model calculation. In this calculation the Σ-hyperon-nucleus interaction in the intermediate state is approximated by an effective potential acting on the Σ hyperon. It is found that very good fits are obtained with a potential of central depth around 37 MeV. This value implies that the Λ-and Σ-hyperon-nuclear potentials are of similar strengths. We show that such a result is consistent with the data on free (Σ+/-,p) and (Λ,p) interactions at low energies, and data on hypernuclear binding energies. This potential depth is also consistent with the meager information on the effective potential felt by Σ hyperons in medium-weight nuclei. There is therefore no evidence in the reaction observed for any final-state (Λ,p) resonance as postulated by Bugg, Bhatt, and Cohn.