pip. N^!* 22Y* CORALVILLE RESERVOIR — CALDWELL 97 



SITE 13JH4 



Site 13JH4 consists of seven conical and a single linear mound 

 situated upon a densely forested ridge top formed by the headward 

 cutting of the northern and southern forks of an unnamed eastern 

 affluent of the Iowa River (fig. 10). The structures range down the 

 ridge top following a northeast-southwest direction (fig. 14). The 

 mounds vary from 20 to 32 feet in diameter and reach a maximum 

 height of 2.5 feet. The easternmost and the westernmost had been 

 previously disturbed. Conical mounds No. 4 and No. 6, and the linear 

 example (No. 7), were chosen for excavation as the most accessible 

 and the least burdened by brush cover. 



MOUND NO. 4 



The diameter of mound No. 4 is 25.7 feet and the elevation is 2.5 

 feet. The mound was approached via a trench oriented to section 

 the structure adjacent to its medial line. The trench, based upon a 

 5-foot square unit (0.5 foot vertical control), reached a maximmn 

 length of 20 feet. A single offset (one 5-foot square) was excavated 

 to sample the apex and central portion of the mound (pi. 18, 6). 



STRATIGRAPHY 



Two distinctive strata are present (fig. 15) : 



A. A basal stratum of compact yellow-brown loessic clay similar to that appar- 



ent in the adjacent countryside. Included are numerous small pockets of 

 ash, charcoal, and occasional occurrences of aragonite (possibly caliche) 

 crystals. Leached products of the subsoil have created a pervasive 

 "chalky" appearance throughout the exposed portion of the stratum. These 

 deposits form a distinctive dome or coi-e, but not concentrically oriented 

 with the observed outline of the superstructure. This underlying stratum, 

 in detail, is composed of two transcending units : 



1. An upper layer of distinctive ash and aragonite "pockets" inclusive in 



a dense, friable clay matrix. 



2. Beneath 1, the chalky "color" (cf. 13.TH3) is more pervasive, but the 



"pockets" are not present. It seems probable that 2 is undisturbed sub- 

 soil, penetrated by the leached products of 1. 



B. The superstructure of the mound is distinctly less friable than the under- 



lying stratum A, but is of a very similar matrix. Stratum A is separated 

 from stratum B by a moderately abrupt transition, but a disconformity 

 is not present. 



It is apparent that mound No. 4 was constructed in two units, the 

 lower containing ash, charcoal, and possibly, fragments of limestone, 

 which are currently evident as aragonite. The matrix of the latter 

 unit appears to be essentially similar to the indigenous subsoil into 

 which it transcends. The inclusions, lacking distinctive patterns as 

 they do (excepting possibly the putative limestone), suggest origin 



626583—61- 



