Abstract: A lateral mobile storage system is disclosed in which the weight of the rear, fixed storage unit rests upon the foot of an anti-tip underlayment. The anti-tip underlayment has an arm extending forwardly upon which rests the rear track for the mobile storage unit held in correct alignment thereby with the fixed storage unit. The mobile storage unit carriage includes a rearwardly extending finger which engages a retainer on the anti-tip underlayment to prevent the mobile storage unit from tipping forwardly. The components are provided in modular lengths and need not be affixed to the floor.