They are made of quartz and quartzite gravel, and are located midway between the car park and the Organ Pipes. They are stated to be part of a deep lead—an ancient stream bed buried by a lava flow, and later revealed by the downcutting of Jackson Creek. Deep leads were mined for gold in Ballarat during the Gold Rushes. The volcanic soils in the park formed above basaltic rock base are found in the valleys and have gentle or flat slopes. Soil types have been classified as zonal types comprising red-brown earths (dominant type in the park with low permeability), grey duplex soils in flat areas (with high permeability) and uniform medium loams (on steep slopes on the southern direction of shallow depth and well drained); azonal soil types consisting of alluvial soils (fertile soils in the park consisting of clay loams to gravels suitable to grow tolerant plant species like river red gum and river bottle-brush), colluvial soils (at the toe of steep slopes of dark grey to dark brown in colour, suitable to grow wide variety of vegetation) and lithosols (reddish brown soils on steep slopes and frequently support boxthorn and indigenous lightwoods ("Acacia implexa"); and other lithosols which are pre-basaltic sands and gravels seen near the foot of Grey Box Gully and in lower slopes of the Jacksons Creek valley. Soils in the park have been subject to erosion, weed growth, human activity and animal burrowing, particularly by rabbits. They are generally found not suitable for plant growth due to their poor water holding property. The degradation of the soils has been arrested with extensive re vegetation. Intense propagation of vegetation of native species, in an otherwise plain degraded area infested with weeds (semblance of native vegetation seen mainly as thistles and boxthorns), started from the time of declaring the area as a national park in 1972. Work continued to remove introduced plants and vermin, and reintroduce natural vegetation and wildlife to the park. As of 2002, large areas of trees and shrubbery began to be re-established, systematic planting of native grass, plants and trees was started, which has created large swathes of kangaroo grass ("Themeda triandra"). The effect of the revegetation project in progress for now more than two decades has created a variety of ecosystems. Seven types of wattle were seen blooming at one time and many other indigenous plants. Six types of vegetation witnessed, consequent to the re-vegetation programme launched by the Park Administration with assistance from FOOPS, are in three landform zones reflecting the soils derived from the underlying geology.