In 1996, a local conservation group called ASEPALECO bought the land from a couple of elderly farmers. They named the reserve after the late Karen Mogensen, a Danish immigrant who together with her husband Olof Wessberg, was instrumental in established the Cabo Blanco Reserve, Costa Rica´s first protected nature reserve.

Since purchasing the reserve, tree planting, fence removal and natural regeneration have all played a role in returning this former patch of farmland back to bona fide jungle. Featuring both primary and secondary transitional dry-humid tropical forest, the Karen Mogensen Reserve protects the headwaters of rivers that provide drinking water to much of the peninsula.

The reserve is also a crucial link in an expanding biological corridor that runs from Cabo Blanco Reserve on the peninsula´s southwestern tip to the Barra Honda National Park, 50km north.
 
White-faced monkeys, howler monkeys, otters, deer, tapir and even puma abound and close to 250 bird species have been identified here, including the rare great curassow which can reach up to 91 centimeters tall. 

The reserve has about 5km of well-maintained hiking trails. One trail leads to Bridal Veil Falls, one of Costa Rica´s most spectacular waterfalls which cascades into a refreshing natural swimming pool.