GPS Glitches - Anyone Know What Gives?

I'm hoping someone out there will at some point be able to explain the apparent GPS glitches regarding where state borders show up on Garmin's MapSource software. My on-the-ground Map Points do not agree with the location for those borders in MapSource. For instance, MapSource shows the Wyoming/Utah border point where US Highway 191 crosses just east of Flaming Gorge at N41 00.718 W109 25.397. My on-the-ground map point, reading the border from my Garmin Colorado 400t at 80 ft. showed it at N41 00.718 W109 25.534, a difference of about .1 mile. That's a lot.

When I marked the border near the "notch" of Wyoming and Utah my on-ground reading was N41 00.519 W111 02.814 and MapSource shows the point at N41 00.553 W111 02.726, a difference of 206 feet north/south error and again, about .1 mile error east/west. So, any geocachers out there know what's going on here? I'll see if I can track this down myself but I would appreciate any help.