I lured one near Whiterun by hitting it with fireballs from long distance, then ran towards Fort Graymoor (after it had been cleared of bandits and occupied by the Imperial Legion) likkitty split with the big fella in pursuit. The mammoth came right into the fort and, to my surprise, only one Imperial soldier attacked it! The rest didn't seem interested. Then it charged me so I ran up some steps and hid behind a building that shook from the mammoth's charge! It went back to fighting with a soldier so I pelted it with more fireballs, each one whittling down its health. It turned and charged again, so I escaped behind the building! Finally, a few more fire balls did it in and it keeled over. That was one of the more memorable fights!

I had just cleared out the bandit hideout with the forge and needed the tusks for an quest, shot at the mammoth and took 3% health and two of them charged me.
I run into an open tower where they could not follow me, I raised archery 3 levels on killing them, recovered 14 arrows from one body.

I remember killing one about 3 hours in. I stood up on top of a rock/boulder and wasted all of my magicka using flames then shot arrow after arrow into him and then more flames. Eventually he went down.

I used a Stealth approach.

I hid amongst boulders at a distance and spied three of them hanging out together. I queued up my Illusion magic and sent one into a frenzy, and the other two mammoths and their Giant herder killed it for me. Then I carefully crept up and looted its corpse.

Worked like a charm.

Haha I see what you did there

First time i found a mammoth i didnt realise that where there are mammoths, there are usually giants. so i started attacking the mammoth, feeling like a hero, and then found myself flying over the mountains courtesy of a giant club. Note to self : Dont provoke a giant when youre only level 4.