a preferred embodiment the top surfaces 20 of the frustoconical structures 15 interface with the upper surface 12 such as an artificial turf or a hard playing surface the top surfaces 20 are generally planar and are roughly parallel to the bottom surfaces 18 where the frustoconical structure 15 has a bottom surface 18 that resembles a rook with crenellations the crenellations have upper edges that are generally co planar see fig5 in one preferred embodiment see e g fig1 4 the modules 10 provide mutual support they coordinate with and connect to one another despite having features described below that accommodate thermal expansion and contraction to attach adjacent modules 10 oval female troughs or recesses 44 fig3 are provided in a peripheral edge flange of a module that engage male protuberances 46 in a peripheral edge flange of an adjacent module the oval female recesses 44 are oriented so that they are preferably substantially aligned with a major component of a direction of thermal expansion and contraction when a male protuberance 46 is engaged by a female recess 44 unidirectional relative movement therebetween can be accommodated without the buckling of adjacent modules 10 if desired lugs 50 and grooves 52 fig3 can be provided in the walls of male 46 and female 44 members or vice versa to provide a snap fit engagement mechanism between adjacent modules 10 the lugs 50 and grooves 52 may be defined continuously or intermittently in the sidewall 44 46 optionally a flooring surface 12 can be laminated to the underlayment system 10 in this embodiment the cone array 15 and male members 46 are covered by the flooring surface 12 and the female members 44 exposed when the laminated system is snapped together the sides of the flooring surface butt together thereby creating.