The Cock Rock is an easter egg featured in two GTA games.
GTA San Andreas
Cock Rock is a rock formation found in Grand Theft Auto: San Andreas, west of Verdant Meadows and south of Las Payasadas in Bone County. It is in the shape of a penis, earning it its name. It is easily seen from the airstrip and in high rock formations like El Castillo del Diablo and Arco del Oeste.
GTA Chinatown Wars
A similar rock formation can be found in Grand Theft Auto: Chinatown Wars. However, it is not that noticeable, having a flatter appearance. The Chinatown Wars rendition is situated on the beach of Firefly Island. The rock is not officially known as Cock Rock, but players call it that.