Trying to go back further with Nils Johannes Olsen

Hi, My great-grandfather, Nils Johanes Olsen, was born in Avaldsnes, on the island of Karmsoy in Rogaland County in Norway in 1861. He married Dorothea Marie Sandstrom. They emigrated to the U.S., where he first settled in Wisconsin before moving to Washington. Dorothea died in 1903 and Nils died in 1933 in the town of Carolls Point, Washington. His father was Ole Rasmusen and mother was Berthe Karen Endresdatter. He had a brother, Ole Johan Olsen, and two sisters, Ingeborg, S and Inger O Olsdatter. His grandfather was Rasmus Z Olsen, who was born in 1809. The farm, I believe on which Nils and his brothers were born was called Strompevig. I would love to be able to go back farther in our family history to see who else we are related to and, perhaps, find out a little about the town where he was born and the farm his family owned or on which the Olsens/Rasumusens lived and grew up. Does anyone out there have any information about this they could share? It would surely be appreciated by our family, that's for sure. My father, who died in 1999, finally learned who his great grandfather was thanks to a Norwegian I met, but I lost the other information this good person gave me. We are all proud of our Norwegian heritage, and this is information I would like to pass to my brothers, and my 10-year-old son. Thanks again, Monte Olsen Eugene, OR USA Is there anywhere I could find this information?