Methods and systems for measuring erosion. Systems of various embodiments include a sensor adapted to be placed where earthen material is expected to move and to sense a condition related to that movement (for instance, the position of the sensor). The sensor includes a receiver for receiving a wireless signal (be it acoustic, magneto-inductive, etc.) from another sensor which conveys an identifier for the second sensor. The first sensor also includes a signal generator that generates a second (possibly wireless) signal conveying that identifier and its own identifier. Systems of some embodiments include a second receiver placed outside of the region. If desired, the sensor can determine the signal strengths of the signals that they receive from the other sensor and can convey an indication of the received signal strengths. Furthermore, some sensors include accelerometers, roll sensors, tilt sensors, yaw sensors, magnetometers, etc.