Lyme disease is not just in the eastern US. It is mostly diagnosed in the eastern US because doctors there are more familiar with it. There is a huge under diagnosis problem in the rest of the US. https://www.usnews.com/news/best-states/new-jersey/articles/...

There is actually quite a lot of lyme disease in Northern California. http://ipm.ucanr.edu/PMG/PESTNOTES/pn7485.html