Hole-in-the-Rock is a natural geological

Geology

Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

 formation in Papago Park

Papago Park

Papago Park is a municipal park of the cities of Phoenix and Tempe, Arizona, USA. It has been designated as a Phoenix Point of Pride.-Description:...

, a municipal park

Park

A park is a protected area, in its natural or semi-natural state, or planted, and set aside for human recreation and enjoyment, or for the protection of wildlife or natural habitats. It may consist of rocks, soil, water, flora and fauna and grass areas. Many parks are legally protected by...

 of Phoenix

Phoenix, Arizona

Phoenix is the capital, and largest city, of the U.S. state of Arizona, as well as the sixth most populated city in the United States. Phoenix is home to 1,445,632 people according to the official 2010 U.S. Census Bureau data...

 and Tempe, Arizona

Tempe, Arizona

Tempe is a city in Maricopa County, Arizona, USA, with the Census Bureau reporting a 2010 population of 161,719. The city is named after the Vale of Tempe in Greece. Tempe is located in the East Valley section of metropolitan Phoenix; it is bordered by Phoenix and Guadalupe on the west, Scottsdale...

.

Description

Hole-in-the-Rock is a series of openings (tafoni

Tafoni

Tafoni are small cave-like features found in granular rock such as sandstone, with rounded entrances and smooth concave walls. They often occur in groups that can riddle a hillside, cliff, or other rock formation. They can be found in all climate types, but are most abundant in intertidal areas...

) eroded

Erosion

Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...

 in a small hill composed of bare red arkosic

Arkose

Arkose is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose....

 conglomerate sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

. The sandstone was first formed some 6-15 million years ago, theorized to have been the accumulation of materials sliding off a much higher mountain, which, made of different materials, has long since eroded away, leaving what looks like petrified mud cakes. The tafoni are thought to have been eroded by water. An open, shelter-like chamber in the face of the formation communicates with the rear of the formation via a hole eroded completely through the rock. Another substantial opening exists in the “ceiling” of the chamber. There is evidence that the Hohokam

Hohokam

Hohokam is one of the four major prehistoric archaeological Oasisamerica traditions of what is now the American Southwest. Many local residents put the accent on the first syllable . Variant spellings in current, official usage include Hobokam, Huhugam and Huhukam...

, early inhabitants of the region, used and recorded the position of sunlight

Sunlight

Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

 shining through the latter opening to mark the seasons—notably the equinox

Equinox

An equinox occurs twice a year, when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth's equator...

es and the solstice

Solstice

A solstice is an astronomical event that happens twice each year when the Sun's apparent position in the sky, as viewed from Earth, reaches its northernmost or southernmost extremes...

s, which were marked by carving a slick area (metate

Metate

A metate is a mortar, a ground stone tool used for processing grain and seeds. In traditional Mesoamerican culture, metates were typically used by women who would grind calcified maize and other organic materials during food preparation...

) in the rock. Other positions were marked with boulder

Boulder

In geology, a boulder is a rock with grain size of usually no less than 256 mm diameter. While a boulder may be small enough to move or roll manually, others are extremely massive....

s.

The formation is a popular attraction in the park. The openings and main chamber, near the summit, are easily accessible via a smoothly ascending path that passes behind the hill. It is also possible to climb the face of the hill to reach the chamber, although this is dangerous for the inexperienced. The chamber provides a good view of the city of Phoenix

Phoenix, Arizona

Phoenix is the capital, and largest city, of the U.S. state of Arizona, as well as the sixth most populated city in the United States. Phoenix is home to 1,445,632 people according to the official 2010 U.S. Census Bureau data...

west of the park. A nearly constant wind blows through the openings in the rock.

External links

• Papago Park Facts - provided by the City of Phoenix
• Hole-in-the-Rock - provided by Gemland