The only significant yields came from the original surface layer on the east half of the Crater -- a black and sticky gumbo clay ranging from about one to four feet thick.

In the early era, 1907–1932, companies finally gave up on conventional processing and adopted hydraulic mining to break down the black gumbo.

That method was employed on a grand scale in California, to extract gold, and was already being used by one of Reyburn's competitors on six acres at the north end of the Arkansas diamond field.

Available photos of Reyburn's property show large hoses spurting pressurized water, which carried material through sluice boxes where diamonds and other heavy minerals were concentrated for screening.

In Sam Reyburn's hydraulic testing, the "black gumbo" surface material often yielded about thirty carats per hundred loads, a very high number compared with diamond fields generally.

Because equipment of the early period usually included bottom screens with mesh larger than 1/16th inch, thousands of smaller diamonds were allowed to pass through during testing.

The bulk of these ended up in shallow drainage cuts all over the diamond field and in the big natural drains on its east and west edges.

Since the State of Arkansas acquired the Crater, in 1972, regular plowing on the east side has marked the main field, 30 to 35 acres of easily eroded breccia.

The regular diggers have worked especially hard for recoveries from the east drain, about ten feet deep: runoff from the field buried much of that channel during the early era; bulldozers finished the job while preparing access for a later test.

On the other hand, all available evidence indicates that the Town of Kimberly originated as a land-development venture in 1909, initiated by Mallard M. Mauney and his oldest son, Walter, on their land immediately south of Murfreesboro.

In April 1952, Millar and his wife, Modean, launched their tourist attraction on a small north section of the diamond-producing field.

Howard Millar, an accomplished writer and promoter, stirred unprecedented national publicity and drew enough visitors to sustain the operation.

In 1970, the entire volcanic formation was consolidated by a private partnership, which then reassigned the property to General Earth Minerals (GEM) of Dallas, Texas.

GEM expected to turn the property over for a profit, but ended up heavily indebted to GF Industries (GFI) of Dallas.

More recent research by geologist Dennis Dunn (Ph.D. dissertation 2002) found that the diamondiferous epiclastic rocks range from olivine lamproite to phlogopite and olivine-rich tuffs.

[5] In addition to diamonds, visitors may find semi-precious gems such as amethyst, agate, and jasper or approximately 40 other minerals such as garnet, phlogopite, quartz, baryte, and calcite.