Mountainous region south of the red river delta that stretches south toward the mekong river delta cambodia 2. southernmost tip of vietnam red river 3. country that borders vietnam on the southwest ca mau peninsula 4. a branch of a river that flows away from the main river channel river delta 5. an arm of the south china sea located by northern vietnam gulf of tonkin 6. country that borders vietnam on the west annam highlands 7. river that begins in china and flows southeast across southern vietnam to the south china sea; longest river in southeast asia mekong river 8. a river that originates in southern china and flows across northern vietnam into the gulf of tonkin laos 9. the area where a river flows into a sea; often have rich soil deposits that are good for agriculture distributary