Pilot reported descending to an altitude; then having ATC call and advise they were below the MSA.

Narrative

Descending through about 6;000 on way into Gateway Mesa Airport IWA; I was told to descend to 2;500 ft; I responded to the Controller to descend to 2;500 ft. The descent was VMC and being slightly familiar with the area I knew that there was a ridge of mountains I had to cross before descending that low. I slowed my descent so that I could easily cross the mountains with plenary of clearance; once between the last peaks I was still around 4;800 ft in a slow descent and began to continue to descend to the cleared altitude of 2;500 ft.Passing through 3;800 ft the Controller says Aircraft X immediately climb to 4;300 ft the Minimum Safe Altitude in that area is 4;300. Safety was not compromised and I heard nothing else the entire flight. Landed at Mesa without any complications or notices from ATC. Using the vertical track feature in App I can tell that I descended to 3;568 ft then returned to 4;045 ft. before being cleared to continue descent. Conditions were CAVU VMC and at no time was there conflict with terrain as I made sure that I was clear before descending. Flight originated at ZZZ; top altitude was FL250. In hindsight I should of queried the Controller on the altitude before initiating the descent.