ARROWHEADS
Most of us grow up knowing exactly what an arrowhead is; a triangular-shaped piece of flint affixed to the end of an Indian's arrow, shot with the use of a bow. The image is firmly stuck in our brains. In reality, two classes of such things exist in the archaeological record, and the general term PROJECTILE POINT is now a sort of politically correct archaeological catchall phrase for a sharp, worked piece of silica-rich (usually) rock, like agate or obsidian, lashed to the end of either a spear or and arrow's shaft. So what's the difference?
Our old childhood friend the arrowhead must be functionally small, because the ancient Indian arrow was small compared to the European long bow's arrow or today's modern hunting arrow. Before the Bow and Arrow was introduced into prehistoric North America, the weapon of choice was the atl atl, or spear thrower. The dart hurled by such a device was long and stout, and tipped with a relatively large, reactively heavy streamline stone projectile point. Such a projectile point was heavy, serving to provide ample cutting edges and weight to provide inertia to the shaft when powerfully by the human arm.
An arrowhead, on the other hand, was tiny in comparison, and light. Hafted to a small, thin arrow, these projectile points functioned to be one with the shaft, providing a balance to the arrow when launched by the energy-release of the bow flexing and a string pushing. Having a large, heavy stone atl atl projectile point on a small arrow would effectively force the arrow to suddenly dive once released; Sort of like having a duck with a five pound head trying to fly. It wouldn't work. Rule of thumb: Small projectile point = arrowhead; Large projectile point = atl atl dart point.
Below is a typology of at at and arrow projectile points which can be found in Arizona. Note that it's still OK to have a collection of such and call it your arrowhead collection; people will know exactly what you mean. This being only a tiny sample of known projectile points to be found in Arizona, a good comprehensive book is vital if you are serious about knowing the what, when and where of your lithic find. The best book I've seen on arrowhead identification is OVERSTREET IDENTIFICATION AND PRICE GUIDE TO INDIAN ARROWHEADS, by ROBERT M. OVERSTREET. This indispensable reference book is loaded with photos and detailed descriptions. Order from Gemstone Publishing Inc, Randomhouse Information Group, 1745 Broadway, NY, NY 10001, or on-line at www.houseofcollectibles.com: 496 pages, about $30
NOTE: EARLY DATES ARE GIVEN IN "BP" or before present date, later cultures adhere to the classic dates "BC," before Christ. NOTE: ALL PROJECTILES SHOWN ARE ONLY EXAMPLES OF TYPES FOUND IN ARIZONA.

PALEO INDIAN TYPES

CLOVIS TRADITION. ALL ARE ATL ATL DART POINTS; 11,000-13000 BP. FOUND STATE WIDE

Below are Paleo Indian point types alledgidly found in Arizona. For the most part these have their origins in other regions of North America, but are listed here for possible identification purposes should similar lithics be discovered.
Plainview
Hell Gap

Agate Basin

Scottsbluff
Eden
FOLSOM TRADITION, ALL ARE ATL ATL POINTS,
10,000 BP-11,000 BP
DESERT ARCHAIC, ATL ATL POINTS
8,000-7,000 BP
BASKETMAKER (LATE ARCHAIC?) ATL ATL AND POSSIBLY EARLY ARROWHEADS 2, 200 BP-1950 BP
ANASAZI, MOSTLY ARROWHEADS BUT ATL ATL WAS STILL IN USE, 750BP-1600AD
HOHOKAM PROJECTILES, ARROWHEADS AND ATL ATL DARTS
Early Hohokam projectile points are some of the most elaborate and beautiful points ever made. Some are large, barbed and have T deeply serrated edges and would have made awesome-looking weapons. These projectile points were "clearly made by specialists." Later Hohokam projectile points were much smaller and heavier, and usually triangular shaped. Later Hohokam types were often crude in comparison.
T-RAT STAGE I-V PROJECTILE CHRONOLOGY:
1948-THE FORESEEABLE FUTURE
ca 1955 AD
ca 1960 AD
ca 1963 AD
ca 1966 AD
ca 1969 AD-Present