Airfare to Europe has dropped to upper $400s/low $500s for San Francisco to Amsterdam if you return after August 15. The $485 deal is available into May 2019 with Virgin Atlantic and British Airways offering one stop flights from SFO to LHR on VS, then British Airways from LHR-AMS.
Google Flights shows American Airlines has two stop flights to Amsterdam from Aug-May 2019 for $464 to $508 flying Oakland OAK to Phoenix PHX, and connecting to a hub in the USA or London for a flight to Amsterdam on AA or BA. These tickets priced last night, but I do not see these prices today. British Airways is pricing at $606 for dates I checked.
This Virgin Atlantic ticket price below is a higher $545 simply to show an example of a relatively low fare for travel departure in July with return after August 16, the first low fare return date for these tickets.
Virgin Atlantic/British Airways San Francisco
SFO – LHR – Amsterdam AMS – LHR – SFO