These sturdy and elegant boards are made for us by a local game/puzzle company. They are formed by a black laser-cut grid affixed to a white base. It takes five sets of Treehouse, plus one extra color to play Volcano. Rules are in the book Playing With Pyramids, or online.
Although Volcano can be played on any 5x5 grid, the solid board with raised edges that hold the pyramids in place is really nice for being able to move the game around: turning the board to look from a different angle, or picking it up and passing it to another player.
There are many other games for the pyramids that which use this board. Check online for more info.