Deep (> 40 km) seismic reflection surveys are acquired on land along crooked roads. Using the varying azimuth between source and receiver, the true 3-D orientation of crustal structures can be determined. Applying this method to a survey over the ancient Australian Yilgarn Craton reveals that most reflectors in the lower crust exhibit a systematic dip perpendicular to those in the overlying crust, consistent with lateral flow of a weak lower crust in the hotter early Earth 2.7 billion years ago.