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These include Medicine Lake volcano's summit caldera, the much-eroded Mount St. Helena and Cup and Saucer volcanic centers in northern and southern Napa Valley, and the Little Walker Caldera at the eastern end of Sonora Pass. In addition, the eruption which produced the widespread Rockland Sequence of tephra and ash was likely from a caldera in the Lassen region which was buried and filled in by later volcanic activity. Most of these are very old and unlikely to ever erupt again. 

While calderas are often associated with gigantic explosive eruptions, their name - which means cauldron in Spanish - is really a description of their shape rather than how they formed. While many calderas do form during large explosive eruptions, some also form after large effusive eruptions. For example, Medicine Lake is known for its voluminous lava flows, and its caldera was formed after these flows drained its summit magma storage. This is also what happened at Kīlauea in Hawaiʻi during its 2018 eruption. (USGS photo by Emily Montgomery-Brown: CalVO geologist Wes Hildreth takes notes among the flowers in the heart of the Long Valley Caldera)