Medium Transport; Low Wing; 2 Turbojet Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 11
Situational Awareness; Communication Breakdown; Confusion
Airspace Violation All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Separated Traffic
Procedure
I was working all of our airspace combined up (mid configuration) as I was splitting the airspace off and doing a briefing I noticed a code come off GJT which was Aircraft X.  Denver TRACON normally takes the airspace around 1200Z (0600L) but they never called today.  I called tower and questioned them about the release and they said approach was open; which I told them they never called us to get the airspace.  I then called Denver TRACON who would normally take the airspace and questioned what Aircraft X was doing in my airspace and what was going on because they never called us for the airspace.  The controller said he forgot to call me for the airspace and he did have Aircraft X climbing to 140.  I then released the airspace to them.This is now the second time in a year I have had this happen to me.  I believe a review of their opening checklist may be in order; they need to call and get the airspace before clearing aircraft into it.
ZDV Controller reports of the TRACON not making the morning call to receive a briefing and accept the airspace that was given to the Center the night before.  An aircraft was released into his airspace without his knowledge.