Cornallis's Boulder

Choose one pebble or stone that you can hold and throw . The object grows into a boulder with a 10 foot diameter and flies in a straight line up to 90 feet in a direction you can see before falling to the ground, stopping early if it impacts against a solid surface. If the object would strike a creature, that creature must make a strength saving throw. When the object strikes a creature or object and each creature within 5 feet takes 3d8 bludgeoning damage and is prone. On a failed save, the object strikes dealing half damage and is not prone. The boulder brakes into pieces and the area within 10 feet of where the boulder hits turns into difficult terrain 

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d8, for each slot level above 1st.