Warbler Guy, for vagrant warbler sightings, what's a good resource to check when I travel? Are West Coast vagrant warblers easy to find?

Gus (in Chicago), I'm looking forward to our upcoming birding tour for which I'm guiding you....and here's some thoughts on your questions:

1. I use ebird (ebird.org) as a primary source for checking updated, documented sightings.

So, for example, yesterday was a first record for a Golden-winged Warbler sighting in Sonoma Co., CA (in the SF Bay area where I live):

https://ebird.org/map/gowwar?neg=true&env.minX=&env.minY=&env.maxX=&env.maxY=&zh=false&gp=false&ev=Z&mr=1-12&bmo=1&emo=12&yr=all&byr=1900&eyr=2018

As you scroll down the page at the above link, you can see past sightings have occurred in the nearby Point Reyes National Seashore (to the south of of Sonoma Co.), BUT not yet in Sonoma Co.

I imagine the new record will soon be added to ebird.

2. County by county lists of sightings for CA appear via John Sterling's home page at:

http://www.sterlingbirds.com/california_county_birding_intro.html

See the link to a file here and, then, go to the CA county where you will be birding.

I hope this helps!

Regards, Daniel Edelstein
warblerwatch.com