Melvin Gordon trade precedent: A blockbuster
After his famed career with the Chicago Bears, Mike Ditka moved onto the New Orleans Saints. After two poor 6-10 seasons, he famously proclaimed that he would trade his whole draft class for the opportunity take running back Ricky Williams. They eventually did, sending a whopping eight draft picks to the Washington Redskins for the rights to draft Williams. The deal was massive and had repercussions all around the league, as the Redskins traded the majority of those picks in order to move up themselves in future drafts with the key piece of their return becoming one Champ Bailey. After three short years, Williams was traded to the Miami Dolphins and the Redskins eventually traded Champ Bailey to Denver for Clinton Portis in 2004.
It is extremely unlikely the Chargers could get anyone to trade their entire draft class for Gordon, but as was mentioned above Williams was traded again. The trade to Miami netted the Saints two future first-round picks along with a future third-round pick. Trading eight draft picks for Williams was very clearly a huge mistake, but the Saints were able to somewhat bounce back by getting those three picks. With most people looking at Gordon as top five or six at his position, a similar package like what the Dolphins gave up for Williams should be the minimum for the Chargers.