Abstract: An olistostrome is an impotant tectonosedimentary unit common in melanges. Its (internal) geology and contact relationshipsprovide valuable information about the geological evolution and engineering geological evaluation of the area. In this respect, anarea of 105 sq km, including the Yayla olistostrome (a geological units in the Ankara melange), is mapped and its relationships withsurrounding units are investigated.The Yayla olistostrome is a member of the Ortaköy formation which has two other members, namely the Lower and Upper matadetritics. The oldest member, Lower metadetritic, deposited in a relatively shallow environment and it does not have any biogenic level in the study area. It has well preserved diabase dykes which cut schistosity as well as bedding. It is well observable in Eymir Lake basin. The Yayla olistostrome was placed somewhat later within the Upper metadetritic as a tectonosedimentary deposit whiledetritics were being deposited in a basin which was tectonically active and consequently high sedimentary energy environment.The blocks (olistoliths) of diabase, spilite, deformed pillow lavas, and different types of chert and limestone, metadetritics, andtheir binding materials; volcanic mudstone, calcilutite-calcirudite, and siliceous in places metallifereous materials are the mainconstituents of the Yayla olistostrome.Homoclinal, isoclinal, and in places overturned fods, small scale faults, and joints constitute the main structural elements in theOrtaköy formation which indicate that all three members have been suffered intensively from the Early Alpine orogenic events.