The city is on the east edge of the Ouachita Mountain foothills. Arkadelphia is south of the mouth of the Caddo River. It has two colleges, Henderson State University and Ouachita Baptist University. | The city is on the east edge of the Ouachita Mountain foothills. Arkadelphia is south of the mouth of the Caddo River. It has two colleges, Henderson State University and Ouachita Baptist University. |