By assuming the existence of a novel multipronged string state for D-particles interacting with D-brane intersections in type-IIA string theory, we are able to derive a quantum mechanical description of supersymmetric Reissner-Nordstrom black holes. A supersymmetric index calculation provides evidence for this conjecture. The quantum mechanical system becomes two decoupled conformal quantum mechanical systems in the low energy limit. The conformal quantum mechanics has expected properties of a dual description of string theory on AdS₂ × S².