Editing Yellowstone Caldera (section)

=== Structure of calderas ===
The northern and eastern extent of the first-cycle caldera are unknown due to burial, although it likely reached into the third-cycle caldera, perhaps east of the Central Plateau.{{sfn|Christiansen|2001|p=53}} The Huckleberry Ridge Tuff in the Red Mountains is interpreted as thick intracaldera fill of the [[Island Park, Idaho|Island Park]] Caldera,{{sfn|Christiansen|2001|p=61}} and Big Bend Ridge at the southwestern edge of the volcanic plateau is inferred to be part of its caldera wall.{{sfn|Christiansen|2001|p=61}} A [[fault (geology)|fault]] along the [[Snake River]] and Glade Creek, bounding the northern end of Teton Range and Huckleberry Ridge, is also thought to be part of the Island Park ring-fault.{{sfn|Christiansen|2001|p=62}} It is not known whether any of the first-cycle caldera segments was resurgent.{{sfn|Christiansen|2001|p=63}} 

The second-cycle caldera is known as the [[Henry's Fork Caldera]]. Thurmon Ridge at the northwestern edge of the volcanic plateau is inferred to be its northern caldera wall.{{sfn|Christiansen|2001|p=66}} The fault along Big Bend Ridge was reactivated, collapsing again during the second-cycle caldera formation.{{sfn|Christiansen|2001|p=61}} Although basalt flows bury its southern and eastern boundary, a positive gravity anomaly indicates a circular caldera about {{convert|19|km|mi|abbr=on}} in diameter, with its southern boundary in the middle of the Island Park basin.{{sfn|Christiansen|2001|p=66}}

Robert L. Christiansen inferred that the Yellowstone Caldera is a compound caldera comprising two partially overlapping ring-fault zones, centered on the resurgent Mallard Lake dome and Sour Creek dome.{{sfn|Christiansen|2001|p=35}} The southwest boundary is unconstrained due to post-caldera [[rhyolite]] burial, but he proposed that the south flank of [[Purple Mountain (Wyoming)|Purple Mountain]] and the Washburn Range, along with the west flank of the [[Absaroka Range]], mark the caldera boundary on the north and east sides.{{sfn|Christiansen|2001|p=36}} [[Lewis Falls]], Lake Butte, and Flat Mountain Arm of Yellowstone Lake are also part of the Yellowstone caldera rim.{{sfn|National Park Service}} However, the purported Sour Creek ring-fault zone and the location of the eastern caldera boundary have been challenged. More recent field mappings suggest the eastern ring-fault lies west of Sour Creek dome, closely following the [[Yellowstone River]].{{sfn|Wilson|Stelten|Lowenstern|2018|p=52}}{{sfn|Yellowstone Volcano Observatory|2023|p=29}} 

The most western portion of [[Yellowstone Lake]] is the elliptical {{convert|6|x|8|km|mi|abbr=on}} West Thumb Basin, which includes one of the lake’s deepest areas. It is interpreted as a fourth caldera, formed by a third-cycle post-caldera explosive eruption.{{sfn|Christiansen|2001|p=45}}

[[Image:Yellowstone Major Calderas Map.jpg|thumb|upright=1.7|Yellowstone sits on top of four overlapping calderas (U.S. National Park Service).]]