From Halopedia, the Halo wiki
The Chief attacks Riven Gate, a heavily fortified Banished checkpoint consisting of three massive gates.
The Chief approaches Riven Gate. He can hear a Jiralhanae officer making announcements over a loudspeaker.
If FOB Kilo has been recaptured:
If FOB Kilo has not been recaptured yet:
The Chief engages the Banished troops outside of Riven Gate.
After eliminating the Banished guards patrolling Riven Gate's perimeter, Chief uses his Grappleshot to get over the outer gate (or scales the cliffside to go around it) and engages the Banished troops on the other side. A Phantom arrives and drops off hostile reinforcements. The Chief fights his way across Riven Gate, freeing a trio of captured Marines along the way. The grateful Marines aid him in his task.
The Chief breaks into a gatehouse and lowers one of the three gates.
The Chief fights his way to another gatehouse. He proceeds inside and lowers another gate.
Phantoms and drop pods are deployed, bringing additional enemies. The Chief deals with them and proceeds to the last gatehouse. He goes inside and lowers the final gate.
He starts heading for the generator.
A Banished Phantom arrives and deploys more enemy reinforcements. The Chief eliminates them, then heads to the power station.
If the Chief starts to leave Riven Gate without destroying the generator:
The Chief enters the power station. The generator itself is located in a secondary chamber built within the cliffside. A Special Operations Sangheili guards the access tunnel, while a Sangheili Ultra and a pair of Kig-Yar Raiders guard the generator room.
The Chief kills all the Banished inside the power station. He then uses a control console to expose the generator, which he promptly destroys, ensuring the gates remain lowered.
Mission is completed.