Medium Transport; Low Wing; 2 Turbojet Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 11
Confusion; Distraction; Situational Awareness
ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Provided Assistance
Human Factors; Procedure
I got off the land line and heard the radar controller issue a turn to the right for Aircraft X that was descending to 140 and about to enter an MIA polygon of 158. I saw what was going on and told the controller to also climb the aircraft; in which the Controller then climbed the aircraft to 158. The aircraft did appear to enter the 158 polygon before being level at 158.The aircrafts' routing showed QUIRT; DIJ. The R-side controller mentioned that the route was checked against the MIA polygons (prior to the aircraft checking in) and that the R-side controller thought 140 was a safe altitude to assign. Traffic volume was extremely high for this sector; including DIJ; IDA; AFO; RXE; 46U; PIH and BPI airports. During this busy session of traffic we had numerous instances in which the controllers on Sector 16 changed routes of aircraft after hand off without coordination. I'm not sure if this is something that happened with Aircraft X; but it makes me wonder since my R-side controller thought the original route was clear of the 158 polygon.It would help during high traffic volume times such as this for the solar eclipse to have standard routes for DIN arrivals so that we can have a smoother and more efficient operation. It would also be helpful to put all of the departures on the LAMON departure procedure to keep aircraft clear of JAC arrivals.
Salt Lake Center Controller reported that an aircraft came close to descending below a Minimum IFR Altitude but did not.