Quartz crystal ignimbrite can be seen on the surfaced at many points along the rapids of Sungai Endau. Ignimbrite has a spectacular genesis as it is volcanic but not of the lava kind. The formation is known as "ash flow eruption". This is the most violent type of volcanic convulsion. During an eruption, hot gas is released from the earth.

The high temperature gas carries sand-sized crystals of quartz and shards of glass, fragments of pumice and larger pieces of pre-existing rock. Eventually the heavier particles would begun to settle, after retaining enough heat to weld themselves together.