At first, crops in the Delta reflected different soils – orchards in the northern, more elevated soils and potatoes, beans and onions in the deep peat of the southern islands. Several factors caused waves of changes, one being debris from hydraulic mining, which raised the riverbed of the Sacramento River and caused stone fruit trees to give way to Bartlett pears, which could tolerate the higher water table. Changing market forces during the span of the reclamation period, also determined the ratio at which Delta crops were grown, as did technological developments such as refrigeration and the shift from railroads to trucking. Potatoes and asparagus have been signature crops in the Delta, and, together, their widespread cultivation—with asparagus gradually replacing potatoes—spans the entire period. These crops also pioneered new marketing techniques and, in the case of asparagus, introduced vegetable canneries to the Delta. Sugar beets were not grown on a large scale until World War I, but this crop is also an important part of the Delta’s agricultural history.