Answer Brief
Boulder County plows and patches the subdivision streets it maintains but resurfaces only a short list. Owners pay for the rest, usually through a district they vote in, so on most county-side Gunbarrel parcels the road is already a tax-bill line or a cost no district has been voted to cover.
Comparison Guide
Niwot and Gunbarrel look like the same house at the same price on Zillow. They're not, and the mailing address and the town name both hide the one thing that actually decides between them: the school district, which runs by parcel, not by name.
Boulder
Gunbarrel is a Boulder-area pocket that keeps Boulder Valley (BVSD) schools while costing less: detached homes run roughly the low-$800Ks to about $1.1M vs a Boulder single-family median of $1,299,900. The catch is the parcel's jurisdiction, part City of Boulder, part unincorporated county.