After the drill scans the first five obelisks completely, you will encounter a large stone gate. A few feet beside the gate, there will be a military laptop, which you will need to acess in order to use the Vanguard, a quadrotor drone similar to the Vulture that fires rockets and machine guns.
You will need to destroy all five obelisks in order to get to the next area, and do not fret if the Vanguard is destroyed; it happens, and it will respawn in a short period of time. After you destroy all five obelisks, the achievement will unlock and the gate will open; there will be nearly no Cryptids left to kill after this.
Please list the errors before voting negative, and have fun unlocking!