the land available to grow grapes, impacts open space and natural habitats, and precludes other land uses. Land-use regulation in California places limitations on the types and locations of land development. Many land use restrictions and permitting requirements do not apply to underground space. As of 2004, there were an estimated 130 to 150 caves used for wine aging, barrel storage, and tasting rooms in Northern California. Marketing Marketing is an important component of the modern wine industry, and many caves serve varied marketing and public relations functions. Recently constructed caves contain commercial and private kitchens, wine libraries, concert and exhibit halls, staff offices, elevators, restrooms, and other amenities. Some have high-end interiors, including ceramic and stone flooring, masonry-lined walls and ceilings, sculpture and artwork, mood lighting, fountains, waterfalls, and chandeliers. At Stag's Leap Wine Cellars, a Foucault pendulum swings continuously across a bed of black sand in the central exhibit hall. Wine cave construction The challenge for the design and construction of most wine caves is to create a fairly wide span in weak rock with low cover. The size of a typical wine barrel storage cave is 13 to 18 ft (4 to 5.5 m) wide and 10 to 13 ft (3 to 4 m) high. Constructed caves, however, range up to 85 ft (30 m) in width and 50 ft (15 m) in height; difficult to achieve in poor quality rock. In areas of complex geology, good portal sites are hard to find. A typical wine cave is constructed with two or more portal sites, for safety and operational reasons. At least one portal leads directly outside, but in many cases at least one portal makes a direct connection to a winery building. Most portals into the wine caves have rock/soil overburden heights less than 0.2 times their entrance heights and widths. The height of the portal face normally ranges from 12 to 20 ft (3.5 to 6 m). The portal areas are seldom stripped of the loose soil material and the portals are cut from the native ground surface using excavators. The side slopes of the portal are often laid back to 0.5H:1V or steeper, and the portal face is excavated to vertical or near vertical. The construction of cave interiors can be complicated by the elaborate curves and labyrinth-style floor plans selected by some owners for their wine caves. As the ground surface slopes upward,