Yes, this is a rose. All other thorny bushes have names as well, of course.

Yup, it's a rose :-) There are a number of wild or native roses that grow here in more rural areas and it could very well be one of those but would to see it later in the season and in flower to ID which it might be.

Thanks you both. They were just on the side of the property, seemed very out of place... 2 plants... I'll post pictures later in the season.

Are those "berries" seeds? Or what purpose do they serve?

Yes, the hips contain seeds.

The hips look horribly like R multiflora. Is that a problem in the region?

The rest of the plant does look the part also. There are places here where this species is living on its own, in fact Jacobson, Wild Plants of Greater Seattle - Second Edition (2008) describes it as

naturalized weedily; common

And sections of western WA and Oregon freeways have it planted as a crash barrier in the median. Thereby establishing a nice long corridor of potential sources for infestation. Including where I-5 passes through the Willamette Valley, a major agricultural production area. And I have seen at least a few instances of this median apparently planting seeding out into pasturage down there.