Probably the most prominent feature of a cavern is the darkness. This plays a very important role in the way animals live in caverns and how they adapt to the environment. A cavern system, if large enough, will have three "zones" based on the level of light it receives. The first is called the "Entrance Zone." This is the area at the immediate cavern opening. Next is the "Twilight Zone," the area that starts at the end of the entrance zone and goes until all traces of light are gone. The last zone is the "Dark Zone." This is the rest of the cavern beyond the twilight zone, where no amount of light ever penetrates. Each cavern will have a different distance for each zone, depending on how large the entrance is and the contours of the cavern. Some caverns may not be big enough to have a dark zone.

Different animals live in different areas of the cavern depending on how well they have adapted to the living conditions. Because the entrance zone is so close to the surface, it is effected by the outside elements. Since it gets direct sunlight and rain, both plants and animals can easily live here. This area of the cavern is used mostly for shelter. The twilight zone, which may not get direct sunlight, is less hospitable. It is close enough to the surface that it is still affected by the outside elements, but provides more shelter and a cooler environment than the entrance zone. Some plant life may still grow here. The animals that live in this zone prefer the cooler, moister conditions. Animals that are found in these two zones are not necessarily cavern inhabitants. They are more like visitors who can also live outside the cavern. However, some may choose to live their whole life in a cavern.

The dark zone is the area of the cavern that requires the greatest degree of special adaptation in order to live there. It gets absolutely no light, is not effected by outside elements and has a constant temperature and fairly constant humidity. Through evolution, the animals that live in this area of the cavern have adapted in order to survive. Due to the lack of sunlight, many of these animals have little or no pigment. Many of them also have no eyes or are blind. To make up for the lack of sight, cavern animals have developed other ways to find their way around and to find food. Some have extra long antennae to feel with; others have acute senses of smell and/or hearing.

All of the Sierra Nevada Recreation Corporation caverns go back or down far enough that they have all three zones. The living conditions are similar in each, yet each cavern has some unique qualities.

Boyden Cavern is a horizontal cavern with a large opening allowing easy access. There is a seasonal stream that flows through it which helps keep the environment cool and moist.