Or a good filtration device. Small streams are plentiful at lower elevations.
I've come across rattlers outside of the areas shown on the map, but as TotemLake pointed out, they're quick to retreat from humans just like black bear.
Robinego, I grew up in Wenatchee and our cat used to catch rattlesnakes and bring them into the house to show them off like mice.....and this was right in town.
Funny story if you've got a minute. One day (~circa 1972) my little brother and I were rummaging around in our enclosed back porch while my mom was out there doing laundry (the washer and dryer were out there). We got into some stored firewood and found a small rattler, probably dragged into the house by the cat again.
Mom FREAKED!!!!! Not out of fear of the snake so much as for fear it would bite one of her kids. She promptly pulled off her pump, and while wildly shrieking, "HELP, HELP! A SNAKE! HELP, HELP! A SNAKE!!!!", she proceeded to beat the snake into 3 pieces with the heal of her pump.
I always wondered what the snake would have been saying if it had a voice. Probably, "HELP, HELP! A MOM!!!!".