Make sure you are using current methods, since the "low acid" tomatoes are different now than the tomatoes of the past, and mean that you need to add a form of acid before canning.
Great sources are Ball Canning recipes/website.
Extension Offices, different states have different websites, and they all have great info for all kinds of food preservation. (here is a free pdf for canning tomatoes:
https://catalog.extension.oregonstate.edu/pnw300 direct link to pdf:
https://catalog.extension.oregonstat...f/pnw300_0.pdf ) The pdf file has times and pressures based on elevation.
National Center for Home Food Preservation (
http://nchfp.uga.edu/ )
Taking classes, I learned that the PNW has a lot of naturally occurring C botulinum spores in the soil, so I'm pretty careful when it comes to canning.