related tags: 292E26 2F5922 364B30 5B6555 5C6159 5D5232 735C1C 858E7D basalt basalts clam croix falls flow flows interstate lava mesoproterozoic midcontinent park precambrian proterozoic rift rock rocks st state system tholeiite tholeiites tholeiitic volcanic volcanics wisconsin 273222 849774