related tags: 2B4228 303C2E 5A6257 5F5333 71A246 738B5D 765E1D 92A17F 95B26E 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 576751