Crush the White Legs

Crush the White Legs is a main quest in the Fallout: New Vegas add-on, Honest Hearts. It is the opposing quest to Flight from Zion, in which the Courier chooses to help the Sorrows and Dead Horses flee Zion Canyon.

Detailed walkthrough
The Courier must speak with Daniel and tell him that they wish to fight and wipe out the White Legs with Joshua Graham. Daniel initially expresses some anger at the decision and will hastily disagree with it. The Courier then appears at the Caterpillar's Mound with Joshua Graham and he will provide details of the situation, explaining that he, the Courier, and a combination of Sorrows and Dead Horse warriors will assault the White Legs encampment at Three Marys.

After talking to Joshua Graham, the Courier joins Joshua and the latter provides the The Way of the Canaanite follower perk. Fast traveling is disabled during this quest, so they have to trek to Three Marys while fighting many White Legs along the way. The White Legs mainly seem to appear in groups of three at predetermined locations.

The Courier must then follow the river south-west towards the Bend Bridge, continue along the river south-east towards the Virgin River, but keep going south. The entrance to Three Marys is just south of the Red Rapids docks along the river. After arriving at the entrance to Three Marys, they must fight their way through to the center of the camp.

After reaching Three Marys' caverns, the White Legs detonate mines from an above rock formation, blocking the direct way to the camp's center (this obstruction will not be cleared, even after the ending). Following this brief cut-scene, Joshua will say that the Courier and he will end this no matter what. He leaves and his follower perk is lost.

The Courier must then go through the caverns to reach the other side of the blockade, reaching the innermost parts of the camp. After reaching the destination, a cutscene initiates with Joshua Graham executing two White Legs. He then makes a brief declaration to Salt-Upon-Wounds, mentioning the fall of New Canaan, Syracuse and Caesar's Legion. He also quotes the Bible, less now than before and speaks in the language of the White Legs.

After this speech, Salt-Upon-Wounds will cry out to the Courier asking for help, claiming that they are the only one who will listen to reason. A choice can then be made to either talk to Joshua or fight Salt-Upon-Wounds. To talk Joshua out of executing Salt-Upon-Wounds, two high level speech checks must be passed. With a Speech level of 75, Joshua can be talked down enough to at least let Salt-Upon-Wounds fight back before he is executed. Passing this speech check but failing the next one results in Salt-Upon-Wounds and two more White Legs attacking after dialogue is exited. With a Speech level of 90, the Courier can talk Joshua out of killing Salt-Upon-Wounds entirely. The ending received will be slightly different than if only one speech check is passed. With the Sneering Imperialist perk, the Courier can dismissively tell Joshua to "put a cap in General Gobbledigook."

After either killing or sparing Salt-Upon-Wounds, the ending cinematic plays, involving all of the appropriate choices that were made. After completing this quest the player character receives the O Daughter of Babylon achievement/trophy. Despite this being the staying option, Daniel, Joshua Graham, Waking Cloud, Follows-Chalk, and White Bird will not remain in Zion. Their clothes and other ending gear (such as Joshua Graham's scripture) can be found in the final footlocker, just before the Courier enters the southern passage to return to the Mojave Wasteland.

Bugs

 * A glitch can occur when after the cutscene that plays at the end of the Three Marys' valley, Joshua will turn hostile, causing the quest. The solution is to open the console as the screen fades from black, selecting Joshua and entering "setav aggression 0". This will allow the final dialogue to take place as it normally should. Sometimes Joshua will turn hostile before the scene has a chance to fade in, still causing the quest to fail. Manually save before reaching the cutscene marker, located just passed the oven that can be seen on the right.
 * If Joshua is too far behind the player when the rock detonation occurs, you may be notified that he has left your party and lost his perk, but he will not initiate the dialogue telling you to look for another way around, and when you reach Salt-Upon-Wounds, Joshua will not be there, and you will be unable to move or interact. You can solve this by waiting for Joshua before you enter the area and kill him, it will fail the mission but will activate a new one and you can fast travel and get the map to get out of Zion (you will NOT get any or the items at the end but you will keep your save) or reload a save before Joshua leaves your party. (On PC, there may be another possible workaround. Open console with ` and type tcl to toggle no-clip, then phase around the walls to bypass the point in which the cut-scene would activate. Speak directly to Salt-In-Wounds and agree to talk Joshua down, then pass the Speech checks to resolve the situation peacefully. Doing this will cause the quest to complete and initiate the ending.)
 * If you reload the last autosave where you exited Three Marys' caverns immediately after killing Salt-Upon-Wounds while the end scene music is playing, it will continue to play throughout the battle leading up to the next confrontation with Salt-Upon-Wounds.
 * When traversing the lower path instead of the upper path in the canyon, after a White Legs tribal is assassinated on the top cliff it may turn ragdoll after hitting the ground and injure the player.
 * In some cases, if you don't part ways with Waking Cloud before being transferred to Joshua, he will not start a dialogue with you, you are stuck and you will have to reload a previous save.
 * Sometimes, when Joshua leaves you to move on ahead after the rock detonation, he leaves you his entire inventory, including his Companion Ammo. When this happens, at the end of the trail, there will be a scene where Joshua will kill some White-Legs and confront Salt-Upon-Wounds, but he won't actually do anything because he has no ammo. In order to continue this scene, you need to use the console on him and additem 00176e54 1. Or you can use the console command "enableplayercontrols" to allow you to kill the two White Legs and then talk to Salt-Upon-Wounds.