Am sure if I go back another couple hundred million years back from Wah Wah I could find a bigger one. But what the hell..
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Wah Wah Springs was the largest know eruption in 4.5 billion years.
The Siberian Traps (the area is covered by about 7 million km2 - 3 million sq mi of basaltic rock, with a volume of around 4 million km3 - 1 million cu mi ;
The Deccan Traps (lava flows is estimated to have been as large as 1.5 million km2 - 0.58 million sq mi, approximately half the size of modern India over a million years) might have been larger - but may have just been the volume of lava flow and that they erupted for 100ds of years. These two events were basalt flows (like Hawaii), not explosive events.
And the largest mountain range in the world was is now known as the Iron Range in N WI, U P of MI and MN. at one time.
The largest deposit of Float Copper in the world is in the Keweenaw Peninsula in the U P of MI. The rift along the shore of the Big Lake up there is evidence that at one time N America was once nearly ripped in two. If one flies over the shoreline of the great lakes you can see the old water level lines/older shore lines, when the water level was much higher.
And the portion of Scotland above Loch Ness was once part of N America.
So there is that too.
As far as California? Who cares.