Ferocactus viridescens

Ferocactus viridescens is a rare species of barrel cactus known by several common names, including Coast barrel cactus and San Diego barrel cactus. It is native to southern California and northern Baja California. Most of its native range is in San Diego County, California, where it is threatened by development, agriculture, and other alterations in its habitat.

This cactus is spherical, oblate, or nearly cylindrical, is usually wider than tall, and less than 30 centimeters in height. The flesh is bright green and arranged into several ribs covered in arrays of long spines. The spines stick straight out and may curve a bit, and are red when new, dulling to gray or tan. The cactus blooms in yellow to greenish flowers with red or pink scales. The fruit is yellow or red.
Cultivation: They are summer-growing and pretty easy plants thought slow to start. They are suited for any rich, well drained soil  such us clay, pumice, lava grit, and only a little peat or leaf-mould. If potted, repot them preferably in the spring, if their roots become cramped.  

Generally, they should be repotted every other year in order to provide fresh soil. However, this doesn't necessarily mean they'll need larger containers. Fill about a quarter of the pot with broken crocks, gravel, etc. to promote good drainage. After repotting, do not water for a week or more. Water regularly during the aestival growth cycle (this plant need plenty of water, but do not overwater and let their soil dry out between waterings), and also needs to be avoided wetting the body of this plant while it is in sunlight. 

A wet cactus in the sunlight can cause sun burning which can lead to scares or even fungal infections and death, keep rather dry in winter. No water should ever be allowed to stand around the roots. Feed with a high potassium fertilizer in summer.