Basalt flow

This is an excellent spot to appreciate the variety of textures that volcanic rock can exhibit. If you are comfortable climbing up to access the rock, you can go and examine it up close. The many small holes in the rock are the vesicles where gas and steam would have escaped the lava as it surfaced and cooled. Volcanoes can release large amounts of volatile gas into the atmosphere as they erupt, and these small holes are evidence of that process. (This is also a reason that volcanic rocks typically make effective aquifers—their porosity allows them to retain a lot of water. It is also why pumice stone is light weight.) Try to find some of the round 'pebbles' embedded in the basalt. These are known as amygdules, and they occur when minerals from the groundwater seep into, and fill, the vesicles.