There is an extremely rare site in the photo above, at least in recent years — two DC-7 air tankers on active duty at an air tanker base in California. CAL FIRE has arranged for them to be on contract so that their 23 S-2T air tankers can rotate in for their annual maintenance. The wildland fire season in the state does not appear to be ending, so they had to do something to provide the needed maintenance for their airborne firefighting fleet while the fire danger remains high.
The state of Oregon routinely uses DC-7 air tankers, but the federal government stopped contracting for them a number of years ago.
Meanwhile, the U.S. Forest Service in recent days has had a couple of P2V air tankers on duty. Yesterday Tanker 910, one of the two DC-10 11,600-gallon air tankers operated by 10 Tanker Air Carrier, was brought over from Albuquerque to be available at Santa Maria, California.