Worth noting Trump came in third in Berkeley in 2016, which is something that happened in very few other cities and locales (no matter how Democratic) in the country.
Third?!?! Who beat him (other than Clinton, I mean)? Gary Johnson would make sense in most circumstances, since he beat all other third-party/independent candidates (Evan McMullin would make sense in a hypothetical, heavily Mormon town - though then again, Trump would still beat Clinton in such a jurisdiction), but I can actually see Jill Stein (given how progressive Berkeley is) coming second in the city.
Jill Stein came in second. She also came close in Oakland.
BerkeleyClinton 57,750 90.4%
Stein 2,947 4.6%
Trump 2,031 3.2%
OaklandClinton 158,926 89.4%
Trump 8,470 4.8%
Stein 6,816 3.8%
As for OP's question, it's a tossup between Berkeley & Arcata. If I had to pick, I'd go with Arcata. And no, it has nothing to do with the 2018 CA Senate results.
Fun fact: Jill Stein got 10.1% in Arcata, the only California town she got double-digits in. Point Arena is close behind at 9.7%
Wouldn't be surprised if Arcata was her best city nationwide (Kalawoa County exempted).