Most distant national park on a freeway guide sign

[Kniwt]

I'll nominate Great Basin National Park, signed on I-80 east way back in Fernley, Nevada, about 350 miles away, give or take a few. Street View image:


Non-freeway guide signs welcome, too, I suppose. Might the Grand Canyon be signposted farther away?

[agentsteel53]

I can't think of any offhand, mainly because Nevada seems to be a unique geographic example.  a sparse road network, and here I-80 swings northeast where US-50 (via alt US-50) heads east to the park.

I believe that Yellowstone is signed from I-90 in Sheridan, WY but that's only about 160 miles.

[NE2]

Delaware Water Gap doesn't count.

[Mapmikey]

I could've sworn there was a Yellowstone Nat'l Park sign in Nebraska on one of their upcoming attractions signs they have up and down I-80.  Since I just got done driving much of this EB the other day I would not have seen it but I drove it WB in 2010 which is when I thought I saw it. 

The closest I can find on street view now is this location (view in new google maps then dial back the clock a couple years) which very recently was replaced with a sign that does not mention it.  This is 40 miles east of Ogallala, or about 640 miles via US 26 as they suggest.

http://goo.gl/maps/mhd0A

Mapmikey