Why do they pronounce Arkansas like "Arkansal"?

First of all my fathers own home town is also just near Conway, Arkansas. As to how Arkansas is pronounced I don't know why you're hearing a "L" on the end. The "S" in Arkansas is actually silent. It really sounds more like 'Arkansa'. As to why it's pronounced that way I have no idea, it just is. In the American language many words sound differently then they are spelled. I've always heard that the American language is the most difficult to learn because we have so many ways to use our alphabet and so many letters are silent in words. I hope this helps you to understand a little better.