Cepas are expanding pit terraces created around trees planted on a slope.  When the seedling is first put in the ground, a bit of the hillside is hoed down to create a circular terrace with a lip at the downhill side to hold in water.  As the trees grow, farmers continue to hoe down the hillside, enlarging the cepa.

Farmers take advantage of gravity during the formation of cepas, just like they do during the formation of tablones.  The terraces around the trees trap water and debris flowing down the hillside, irrigating and feeding the trees without any work on the part of the farmer.

I love all of the terrace ideas presented in Gene Wilken's book, but he does include a word of warning --- slope management requires constant maintenance or it can cause dangerous conditions!  Everyone in my area knows about badly built settling ponds constructed in strip-mined areas, and about the disasters that ensue when the dams fail and downstream houses wash away.  Although I find terracing intriguing, I think I'll kick these ideas around for awhile before putting them into practice.