No, that's not a terrifying hole into the underworld; it's a terrifying hole playing an important purpose.
That 72-feet-wide and 245-feet-long hole is the Lake Berryessa spillway, a sort of oversized drain for the Monticello Dam in Napa Valley, California. The water drains out into the Putah Creek below.
Due to the state's extreme drought, the spillway hasn't served its purpose since 2006. However, the region has received record rainfall in January and February, filling the dam to its safe maximum limit, or the point at which the spillway goes into service.
The rainfall and the spillway have brought a significant amount of water to the area, as the drone footage above shows. In addition to getting up close and personal to the spillway, the drone shows off how Putah Creek's various docks and marinas (not to mention the area's wildlife) have benefited from all the water.