Here is the full list of all 46 Rango achievements worth 1,000 gamerscore. It takes around 6-8 hours to unlock all of the achievements on Xbox 360.
Complete Jenkins Cousins' Homestead
Complete Water Train
Complete The Forbidden Mine
Complete Land of Giants
Complete Rodent Clan
Complete The Return of Rattlesnake Jake
Complete Zombie Invasion
Complete Nowhere & Back
Complete Alien Showdown
Complete the game in medium mode
Complete the game in hard mode
Complete hard mode and gather all unlocks & all collectibles
Collect 1000 Sheriff Stars
Collect 10 000 Sheriff Stars
Collect 100 000 Sheriff Stars
Collect 150 000 Sheriff Stars
Collect 200 000 Sheriff Stars
Complete a tale using only your gun
Complete a tale without dying
Defeat 20 enemies using manual aim
Defeat a shooter without using your gun
Defeat 500 enemies
Defeat 1000 enemies
Defeat 100 enemies with melee attacks
Defeat a huge charging rabbit using only melee attacks, without taking any damage from him
Lure a Jumper to land on a shotgun shell
Launch an enemy with an uppercut then shoot him three times
Launch 10 enemies off the train in Water Train
Acquire the Spreadshot and take out 10 enemies with it
Acquire the Launcher and take out 10 enemies with it
Acquire the Blaster and take out 10 enemies with it
Survive the crumbling canyon in The Return of Rattlesnake Jake
Escape the exploding train in Water Train
Ride a bat for an entire level without dying
Ride a roadrunner for an entire level without dying
Defeat Bad Bill in Water Train
Defeat Bad Bill in Forbidden Mine
Defeat Bad Bill in Rodent Clan
Defeat Rattlesnake Jake in The Return of Rattlesnake Jake
Defeat Lars in Land of Giants
Defeat the Alien Probe in Alien Showdown
Defeat 6 zombies with one golf shot
Hit a bullseye in Golden Bullet mode for the first time
Hit 3 bullseyes in a row
Shoot Bad Bill's dynamite bundle before he throws it in Water Train
Smash open 250 crates