Air carrier flight crew was informed after the fact that they landed on unmaintained Runway 2 at YAK (PAYA). This information was not readily available to the crew.

Narrative

We were on final approach for a daytime landing to YAK (PAYA). Upon arrival into the airport area; we determined via radio communications with another aircraft in the pattern that the active runway in use was Runway 2. Additionally; the ASOS report indicated a wind between 5 and 10 KTS that favored Runway 2 and temperatures well above freezing. The other aircraft ahead of us was using Runway 2. There were no NOTAMS regarding any closures or restrictions on Runway 2. I performed an uneventful landing on Runway 2 followed by a taxi to the gate via Taxiway B. The Captain received a phone call from our Base Chief Pilot notifying us of the event.Apparently we had used a runway and taxiway that were 'unmaintained' October 1 through May 1. There were no NOTAMS in the flight paperwork stating this. Additionally; on the airport diagram it only states that Taxiway B; C; and D are unmaintained October 1 through May 1. It states nothing about Runway 2/20. It is only found in an obscure note on our company provided airport briefing material that Runway 2/20 is 'unmaintained' October 1 through May 1. Provide guidance of unmaintained runways and taxiways via NOTAM. In addition; provide this information on the airport diagrams.