The Guadalupe River delta is found immediately across from the Guadalupe Bay site. Overall, geologists have divided this complex delta into two major parts: an older, "Old River" delta whose formation surrounded Green Lake, and a younger "Guadalupe" delta, that partly encloses Mission Bay and remains under construction. Regrettably, there is no radiocarbon estimate to accurately determine the ages of the two main deltas or that of the incorporated subdeltas. Researchers think the delta began to build upon San Antonio Bay some 2,000 years ago. Absent such radiocarbon dates for the delta proper, they must rely upon archeological finds from local digs to calculate the history of the various subdeltas.

It is generally accepted that the oldest delta (formed by the Guadalupe) first prograded to the southeast, and in later periods changed and prograded to the northeast, which isolated the upper part of San Antonio Bay, forming Green Lake. The younger delta, to which this study is devoted, prograded southeastwardly into San Antonio Bay, nearly parallel to the axis of the bay.

In a still later time in its history, the Guadalupe River once more flowed...

An artificial cut was made in 1935; however, that diverted almost half the flow of the river into the upper part of the bay, Mission Lake. Thus another delta is now forming at the mouth of the artificial cut in the protected waters of Mission Lake.
Modern Floodplains and Delta

In conclusion, the historic sequence of subdelta growth south of Mission Lake is now quite well-known. The pattern began with progradation of the "Guadalupe River-Big Bayou" subdelta along the western side of the modern delta area, which later continued to prograde southward, finally dividing into two lobes, one of which stopped development, while the other split again. This last, present-day is labeled the "Traylor Cut" subdelta, that started (and continues to deposit) due to the modern dredging of the Traylor Cut between the Guadalupe River and Mission Bay.

Fortunately, as the pieces notes, this delta is a National Wildlife Area, with many protections in place for the flora and fauna. Hence it will proceed to develop naturally in the future, as the watershed "lungs" of the region.