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 in Verdant Meadows 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.