How do I file for divorce in Washington state on the grounds of desertion?

Given that a spouse can be divorced from the other spouse in WA by simply stating that the spouse does not want to be married with the other spouse any more, asserting that your spouse deserted you may not provide you with additional benefits.

The blank mandatory pattern forms for most WA family law proceedings are free at http://www.courts.wa.gov/forms/ . From that site, there are links to instructions and self-help guides.

If you cannot locate the spouse to have legal documents served on her, you likely will need to ask the court for permission for alternative service, such as by publication. If there is no personal service, the court may not be able to address issues such as division of assets and debts, child support, or parenting plan. However, given that you "have not seen or heard from [your] spouse in over 10 years", those issues may not exist in your case.

You should review your specific facts with your attorney to see your legal options.