There are 5 National Natural Landmarks in Arkansas. Four are forests and one is a spring.

Big Lake National Wildlife Refuge

Mammoth Spring

White River National Wildlife Refuge

Lake Winona Research

Roaring Branch Research

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Arkansas National Natural Landmarks (clickable map)

Name	Image	Date	Location	County	Ownership	Description
Big Lake Natural Area		1974	35°54′48.61″N 90°7′3.4″W / 35.9135028°N 90.117611°W / 35.9135028; -90.117611	Mississippi	Federal	Forest area within Big Lake National Wildlife Refuge.
Lake Winona Research Natural Area		1976	34°42′36.66″N 94°25′27.81″W / 34.7101833°N 94.4243917°W / 34.7101833; -94.4243917	Saline	Federal	Pine forest near Lake Winona (Arkansas); part of Ouachita National Forest.
Mammoth Spring		1972	36°29′52″N 91°32′09″W / 36.4978°N 91.5359°W / 36.4978; -91.5359 (Mammoth Spring)	Fulton	State	The largest first magnitude spring in Arkansas, it is connected underground to the Grand Gulf State Park in Missouri.
Roaring Branch Research Natural Area		1976	34°22′22.8″N 93°58′40.8″W / 34.373000°N 93.978000°W / 34.373000; -93.978000	Polk	Federal	Steep ravine with a virgin forest in Ouachita National Forest.
White River Sugarberry Natural Area		1974	34°21′0″N 91°6′0″W / 34.35000°N 91.10000°W / 34.35000; -91.10000	Desha	Federal	Virgin hardwood bottomland forest in White River National Wildlife Refuge.

• List of National Historic Landmarks in Arkansas