I haven't been out to Roslyn Lake in years, so I am speculating that the grove of trees south of the road is fenced off and PGE Park entrance (East) has been gated shut since they drained the lake. It is remote, but mostly private property out that way. I have a feeling he initially didn't take her out there to kill her, or the initial drive would have probably been straight up to Larch Mountain not to Roslyn Lake. He probably stopped by Dodge Park to dispose of the Apron and stuff in the front seat, plus there are Honeybucket toilets where you can get hand sanitizer or throw things in the toilet. I am not sure if the main bathrooms are open this time of year, but there is a building on site.
In my experience, everything that is round or cylinder (chapstick) that isn't in a cup holder or in the glove compartment tends to roll under my seat.
I haven't been out to Larch Mountain, but I believe the last gas stations going East are either the 257th Shell on Stark or the two gas stations on Frontage Road, where the second gas station charge occurred. Next Gas station on I-84 would probably be Cascade Locks.
Now if all 4 casings were in the car, i think no matter where they ejected they probably bounced off something and ended up on the floor. I am just curious about the extremely loud sound a gun makes in an enclosed area. I have never fired a 9mm, but I am sure his ears were ringing. Gunfire out near Dodge Park and Roslyn Lake are not as common as they are out at Larch Mountain. Dodge Park and Roslyn Lake have homes around there and Fishermen. Thompson Road just happens to be on a not so busy road, and the fisherman don't show up there anymore, because the lake is drained.
I can't find the link, but I know there was a person target practicing killed in that area up on Larch Mountain. I remember a couple of teenagers shot and killed someone, on purpose with an M-16, from the trees while the guy was target practicing. I believe the year was around 1993-1995. So Larch Mountain would have Hunters and Target Practicing going on.