DunDraCon, the west coast's longest running gaming convention, is celebrating it's 40th anniversary this approaching 2016 Presidents' Day weekend February 12th to 15th.
The convention started in 1976, but missed a year in 1981 as a result of the hotel venue changing ownership and no longer hosting conventions. (The DDC organizers did hold "DunDraClone" Labor Day weekend in 1981, which was my 2nd ever D&D convention)
Since 1992 DunDraCon has been held at the Marriott Hotel in San Ramon, California. Our gaming group has ran our games there at every convention except 2014, and I attended every one in San Ramon to different degrees except 2005.
(A brief history of DunDraCon)