My maternal grandmother died due to complications giving birth to my mother (also now deceased) in 1939. The family story was that Mary Shanks (born around 1915) was found on a doorstep and adopted. She was born around 1915, I tried getting a birth certificate from the state of Washington, but they do not have any records. Any ideas how I can verify a date of birth and/or adoption records? I'm new to this research.