@@ -71,6 +71,7 @@ def _apply_contacts_source(self, source):
         source has another (the `basal_contacts` role). Each one is kept.
         """
         from_geology = source == layer_roles.CONTACTS_FROM_GEOLOGY
+        guessed = False
         self._loading = True
         try:
             if from_geology:
@@ -100,6 +101,7 @@ def _apply_contacts_source(self, source):
                     self._guess_basal_contacts()
                     layer = self.basalContactsLayer.currentLayer()
                     field = self.unitNameField.currentField() or field
+                    guessed = layer is not None
             self.basalContactsLayer.setLayer(layer)
             self.unitNameField.setLayer(layer)
             if field:
@@ -108,6 +110,11 @@ def _apply_contacts_source(self, source):
             self.useZCoordinateLabel.setVisible(not from_geology)
         finally:
             self._loading = False
+        if guessed:
+            # The guards of the pickers skip a change while `_loading` is set,
+            # so save the guessed layer here
+            self._write_first_picker(layer, field)
+            self._persist_selection()
 
     def _add_contacts_source_combo(self):
         """Add the choice of where the basal contacts come from."""
@@ -287,6 +294,8 @@ def _guess_basal_contacts(self):
             layer = self.data_manager.find_layer_by_name(basal_match)
             if layer:
                 self.basalContactsLayer.setLayer(layer)
+                # setField does nothing for a field that is not in the layer of the picker
+                self.unitNameField.setLayer(layer)
                 fields = [f.name() for f in layer.fields()]
                 fmatcher = ColumnMatcher(fields)
                 if unit_match := fmatcher.find_match('UNITNAME'):
 
@@ -31,6 +31,7 @@
     StratigraphicLayersWidget,
 )
 
+from loopstructural.main import layer_roles
 from loopstructural.main.workflow_mode import WORKFLOW_MODE_LABELS, WORKFLOW_MODES
 
 from . import checks
@@ -168,6 +169,25 @@ def __init__(self, parent=None, **kwargs):
         self.tabs.setCurrentWidget(self.tab)
         layout.addWidget(self.tabs, 1)
 
+        # With contacts from the geology polygons, the "Source layers" tab has
+        # the geology picker, so do not show a second one on the column tab
+        roles = self.data_manager.layer_roles
+        roles.attach(self._on_layer_role_changed)
+        self._show_column_geology_picker(roles.contacts_source)
+
+    def _show_column_geology_picker(self, source):
+        self.tab.stratigraphic_column_widget.geologyGroup.setVisible(
+            source != layer_roles.CONTACTS_FROM_GEOLOGY
+        )
+
+    def _on_layer_role_changed(self, role, value):
+        if role == 'contacts_source':
+            try:
+                self._show_column_geology_picker(value)
+            except RuntimeError:
+                # the page was deleted
+                pass
+
 
 class FaultsStep(StepPage):
     """Step 3: the fault layer, the fault topology and the adjacency tables."""
 
@@ -289,7 +289,7 @@ def _set_update_buttons_enabled(self, enabled):
     def _build_geology_group(self):
         """Build the group with the geology layer, the unit name field and a
         summary of the unit names that have no match in the layer."""
-        group = QGroupBox("Geology layer", self)
+        group = self.geologyGroup = QGroupBox("Geology layer", self)
         form = QFormLayout(group)
         self.unitsLayerComboBox = QgsMapLayerComboBox()
         configure_layer_combo(
 
@@ -0,0 +1,66 @@
+"""Pytest tests for the source layers of step 2 (`StratigraphicLayersWidget`)."""
+
+import pytest
+from qgis.core import QgsProject, QgsVectorLayer
+from qgis.testing import start_app
+
+from loopstructural.main import layer_roles
+from loopstructural.main.layer_roles import LayerRoles
+
+
+class _DataManager:
+    """The parts of the data manager that the widget uses."""
+
+    def __init__(self):
+        self.layer_roles = LayerRoles()
+        self.layer_roles.contacts_source = layer_roles.CONTACTS_FROM_LAYER
+        self._basal_contacts = None
+        self.basal_contacts_calls = []
+        self.settings = {}
+
+    def set_basal_contacts_callback(self, callback):
+        pass
+
+    def set_structural_orientations_callback(self, callback):
+        pass
+
+    def find_layer_by_name(self, name):
+        layers = QgsProject.instance().mapLayersByName(name)
+        return layers[0] if layers else None
+
+    def get_widget_settings(self, key, default=None):
+        return self.settings.get(key, default)
+
+    def set_widget_settings(self, key, value):
+        self.settings[key] = value
+
+    def set_basal_contacts(self, layer, unitname_field=None, use_z_coordinate=False):
+        self.basal_contacts_calls.append((layer, unitname_field))
+
+    def set_structural_orientations(self, *args, **kwargs):
+        pass
+
+    def logger(self, *args, **kwargs):
+        pass
+
+
+@pytest.fixture
+def contacts_layer():
+    start_app()
+    layer = QgsVectorLayer("LineString?field=unitname:string", "basal_contacts", "memory")
+    QgsProject.instance().addMapLayer(layer)
+    yield layer
+    QgsProject.instance().removeMapLayer(layer.id())
+
+
+def test_the_guessed_contacts_layer_is_saved(contacts_layer):
+    from loopstructural.gui.modelling.model_definition.stratigraphic_layers import (
+        StratigraphicLayersWidget,
+    )
+
+    data_manager = _DataManager()
+    StratigraphicLayersWidget(data_manager=data_manager)
+
+    assert data_manager.basal_contacts_calls[-1] == (contacts_layer, 'unitname')
+    settings = data_manager.settings['stratigraphic_layers_widget']
+    assert settings['basal_layer'] == 'basal_contacts'