I know this doesn't answer where they were buried, but I thought you might like to have the articles. The accident happened in California not SW Washington.
Date: September 08, 1915 Location: Oregon Paper: Oregonian Page 5 column 4 THREE KILLED ON BRIDAL AUTO TOUR
Deputy Collector at Astoria, His Mother and cousin Dead, Wife Gravely Hurt
Driver Kill His Engine on Crossing in Effort to Reverse and Car is Hurled Against Telegraph Pole
Montague, Calif. Sept. 7 Allan Y. Anderson, deputy collector of customs, at Astoria, Or., his mother Mrs. Margaret Anderson, and his cousin, Aaron Anderson, were killed today when their automobile was struck by a passenger train at the Granada crossing of the Southern Pacific Railroad, six miles from here. Mrs. A.Y. Anderson was perhaps fatally injured.
Mr. and Mrs. A.Y. Anderson were married only recently and were on a honeymoon trip toe the Exposition at San Francisco.
The approaching train was hidden from the party by a row of trees and a toolhouse. It was evident that the driver killed his engine directly on the track in an effort to reverse. The car was struck fairly in the middle and hurled against a telegraph pole, the occupants being thrown out. One body lay 65 feet from the car when first aid was offered by a physician who was a passenger on the train.
A.Y. Anderson lived only half an hour after the accident, dying on the train before it reached Montague. Mrs. Margaret Anderson died 20 minutes later while being hastened to a hospital at Yreka.
This article followed the one above:
VICTIMS ARE ALL WELL KNOWN
A.Y. Anderson Native of Clatsop County, Mother Long Resident
Astoria, Or., Sept. 7 A.Y. Anderson, who was killed in an automobile accident in California today, was Deputy Collector of Customs in charge of the Astoria office. He was a native of this county, 35 years old, and two months ago married Miss Eva Shotwell, of Seattle, who was also a victim of the accident.
Mrs. Margaret Anderson had resided in this city many years.
Aaron Anderson, a cousin of A.Y. Anderson, was about 30 years old and unmarried. The party left here last Wednesday to attend the Exposition at San Francisco and San Diego.