The 26-year-old quarterback posted the message on social media on Wednesday ... writing, "This city has shaped the man I've become and I will forever be grateful for the Kroenke family, my coaches, the support staff, and most importantly, my teammates for competing and fighting with me every Sunday."

Goff added, "From the bottom of my heart, it's been an honor to represent the city of LA."

Of course, Jared was just dealt to Detroit in a surprising trade for Matt Stafford over the weekend ... and in an interview with the L.A. Times on Tuesday, he appeared to be perplexed by the whole deal.

Goff said he hadn't talked to anyone in the Rams organization about why their relationship deteriorated so quickly, adding that he found the lack of communication "a little bit" strange.

Goff also said, "As the quarterback, as the guy that’s at arguably the most important position on the field, if you’re in a place that you’re not wanted and they want to move on from you, the feeling’s mutual."

Seems Jared's trying to let it all go now though ... explaining in his note Wednesday, "I couldn't be more excited for this next chapter and am ready to attack this new opportunity that lies ahead."