Amsterdam is on sale for around $470 round trip from Arcata to Mammoth Lakes to San Diego airports in California. Spokane and Tucson have these deals too. This is a widespread sale for travel departures in February and March 2019.
United is the main carrier I see with these tickets from California airports. Some regional airports also have American Airlines. San Diego has all three alliances selling cheap winter tickets to Amsterdam with Delta and SkyTeam offering $470 tickets too.
United Airlines ticket flying United outbound and Swiss inbound
Monterey MRY – San Francisco SFO – Houston IAH – Amsterdam AMS – Zurich ZRH – SFO
All United-operated flights are priced closer to $470 round trip.
I prefer a long haul economy flight directly from SFO to Europe when possible and that is worth an extra $10 to $20 for me rather than connecting at USA airports outside California.