Hi Jenna and thanks for your picture of your mystery flower. It is St. John's Wort. Although there are some cultivars which are probably OK, it is actually considered a Level B invasive plant in Oregon. It shouldn't be too hard to remove through pulling by hand, especially since it is not widespread in your yard yet.

https://www.oregon.gov/oda/shared/Documents/Publications/Weeds/StJohnswortProfile.pdf

Thanks so much for getting it identified and for having a native plant garden in your yard!