The Two Creeks Forest Bed




The world-famous and fortuitous Two Creeks Forest Bed outcrop provides a lesson in interpreting glacial stratigraphy, telling an amazing story of ice advance and retreat, lake level rise and fall, forest bed growth and death, lake level rise and fall,  ice advance and retreat, and lake level rise and fall. The outcrop is located near Two Creeks, Wisconsin after which it is named. The outcrop is a scientific preserve. Visitors should respect a "no hammer, shovel, or sampling" etiquette coincident with the law that applies in most national and state parks. Visitors also assume all risks, including those associated with steep and slumping lakeshore slopes and bluffs. Do not access bluffs from private property without explicit permission.

Enjoy, learn, and marvel! But please respect (as always) photo credits. Gary Larson once commented that his Far Side cartoons are like his children. I feel the same way about photography.


View to north of Lake Michigan shoreline from the boat launch at the end of Two Creeks Drive across Lakeshore Drive, Two Creeks, Wisconsin. Note the Kewaunee nuclear power plant on the peninsula.
Photo Detail: View to north of Two Creeks, Wisconsin's Lake Michigan shoreline.
Caption Credit: John Hoaglund
Photo Credit: John Hoaglund
Photo Date: Friday, May 28, 1999


View to south of Lake Michigan shoreline from the boat launch at the end of Two Creeks Drive across Lakeshore Drive, Two Creeks, Wisconsin. Note the Point Beach nuclear power plant on the peninsula.
Photo Detail: View to south of Two Creeks, Wisconsin's Lake Michigan shoreline.
Caption Credit: John Hoaglund
Photo Credit: John Hoaglund
Photo Date: Friday, May 28, 1999


Shoreline bluff outcrop near Two Creeks boat launch exposing clay-rich glacial till at beach elevation (~580 ft. MSL). Fissility in till resembles clay deposit laminations which, together with high clay content, makes the deposit easily mistaken for lacustrine clay. A little digging, however, reveals many broken, angular pebble clasts and sand seams characteristic of a till origin. Notice large blue (metabasalt) clast near the base of the outcrop.
Photo Detail: View to west of lower till outcrop near Two Creeks boat launch.
Photo and Caption Credit: John Hoaglund
Photo Date: Friday, May 28, 1999


South end of Two Creeks Forest Bed outcrop with cut near top of bluff exposing an upper red till below poorly sorted (generally) beach and nearshore gravel (lighter unit) produced from re-working of the till.  Prominent, dark, O and A soil horizons are clearly seen at the top.  Slumping obscures the lower part of the outcrop.  The beach and nearshore gravel overlying till indicates that a high lake stand (Toleston; 148 m) occupied the Lake Michigan basin after an ice advance that produced the red till.
For glacial phases and associated lake levels, see Hansel et. al., 1985.
Hansel, Ardith K., David M. Mickelson, Allan F. Schneider, and Curtis E. Larsen, 1985. Late Wisconsinan and Holocene history of the Lake Michigan Basin, in Quaternary Evolution of the Great Lakes, P.F. Karrow and P.E. Calkin editors. Geological Association of Canada Special Paper 30. p. 39-53
Photo Detail: View to west-northwest of the south end of the Two Creeks Forest Bed outcrop
Caption Credit: John Hoaglund
Photo Credit: John Hoaglund
Photo Date: Friday, May 28, 1999


Soil, beach and nearshore gravel (the lighter unit), and the red till. Notice that the gravel appears to be coarser grained in both matrix and clast sizes. The gravel is poorly sorted and lacks fissility, whereas the till is unsorted (shows no sorting) and has fissility (horizontal planar partings).  The fissile character of the red till is typical of clay rich lodgement tills.  The slight sorting of the beach gravel indicates that wave action re-worked a till source without transporting the material very far.  Sorting, a characteristic of water-laid sediment, increases markedly with an increase in transport distance.
Photo Detail: Top of bluff exposing soil, a lighter unit, and red till.
Caption Credit: John Hoaglund
Photo Credit: John Hoaglund
Photo Date: Friday, May 28, 1999


Upper red till near the top of the bluff overlies lacustrine sand just visible at the base of the outcrop above slump slopes. Note large erratic within the upper red till. Also notice numerous birdnest holes within the gravel (lighter unit between the upper red till and soil horizons). Bird nesting is restricted to this unit due to its loose bedding and coarser grain size compared to the compacted, clay-rich red till.  The nearshore and beach gravels laterally trace to paleo-beaches slightly inland of the lake.  The red till was historically named the Valders till.  However, the red till observed here above the forest bed, does NOT laterally trace nor time-correlate with red till unit(s) observed at Valders quarry, the type locality located inland from Lake Michigan in Valders, Wisconsin. Instead, this now renamed till (the Two Rivers till) terminates into the Two Rivers Moraine (Mickelson and Evenson, 1975).  The lower till, below the forest bed, does time-correlate with red till(s) observed at Valders quarry, but may or may not laterally trace with those Valders tills. The Valders tills were most likely late-Woodfordian, deposited by the Green Bay Lobe, an ice lobe that was time-correlative with, but regionally separate from, the Lake Michigan Lobe that deposited tills at the Two Creeks outcrop (Mickelson and Evenson, 1975). The distinction between the tills above and below the forest bed, and their differing lateral extents, led to the recognition of a separate glacial ice advance, called the Greatlakean Substage (see Evenson et. al, 1976).

Mickelson, David M. and Edward B. Evenson, 1975. Pre-Twocreekan age of the type Valders till, Wisconsin. Geology, Vol. 3, No. 10. p. 587-590.

Evenson, Edward B., William R. Farrand, Donald F. Eschman, David M. Mickelson, and Louis J. Maher, 1976. Greatlakean Substage: A replacement for Valderan Substage in the Lake Michigan Basin. Quaternary Research, Vol. 6. p. 411-424.

Photo Detail: View to west of till and lacustrine units at the Two Creeks Forest Bed outcrop
Caption Credit: John Hoaglund
Photo Credit: John Hoaglund
Photo Date: Friday, May 28, 1999


Field assistants (wife and daughter) stand at the top of the bluff exposing (from top down) gravel, upper till, lacustrine sands and clays, the Two Creeks Forest Bed, lacustrine sands and clays, and slump slopes that obscure lower till units. Lower till units are exposed at the boat launch outcrop at beach level about 1 mile south. Note log with branch visible in the middle of the section just above slump slopes.
Photo Detail: View to west of Two Creeks Forest Bed outcrop.
Caption Credit: John Hoaglund
Photo Credit: John Hoaglund
Photo Date: Friday, May 28, 1999


Pan right from previous photograph showing log with branch of the Two Creeks Forest Bed interbedded between lacustrine, planar bedded sands with intercalated lacustrine clay. Slumping and washdown obscures the contact between lacustrine deposits and overlying till unit.
Photo Detail: View to west-northwest of Two Creeks Forest Bed outcrop.
Caption Credit: John Hoaglund
Photo Credit: John Hoaglund
Photo Date: Friday, May 28, 1999


Close-up of log and branch of previous photographs with car keys hanging on branch for scale. The dominant tree specie in the forest bed is white spruce, dating to 11,875 radio-carbon years before present. Radio-carbon dating yields the age of tree death, when plant intake of CO2, in equilibrium with the atmosphere, ceases. Most likely the trees died from inundation of water from a phase of proglacial Lake Chicago (Calumet level; 189 m) that existed after the time of the forest bed.
For glacial phases and associated lake levels, see Hansel et. al., 1985.
Hansel, Ardith K., David M. Mickelson, Allan F. Schneider, and Curtis E. Larsen, 1985. Late Wisconsinan and Holocene history of the Lake Michigan Basin, in Quaternary Evolution of the Great Lakes, P.F. Karrow and P.E. Calkin editors. Geological Association of Canada Special Paper 30. p. 39-53
Photo Detail: Close-up of Two Creeks white spruce log.
Caption Credit: John Hoaglund
Photo Credit: John Hoaglund
Photo Date: Friday, May 28, 1999


Close-up of forest bed litter, including roots, branches, bark, twisted logs, pine cones, and carbonaceous material.
Photo Detail: Close-up of Two Creeks Forest Bed (11,875 BP) litter.
Caption Credit: John Hoaglund
Photo Credit: John Hoaglund
Photo Date: Friday, May 28, 1999


Close-up of log (car keys for scale). Note lacustrine sand underlies the forest bed. This implies that a phase of proglacial Lake Chicago (the Glenwood II level) existed before the forest bed grew. The interbedding of the forest bed between lacustrine deposits indicates that the Two Creeks Forest Bed time (ending 11,875 BP) occurred between two lake phases: the Glenwood II high stand (195 m), followed by the Two Creeks low stand (with the forest bed), followed by the Calumet high stand (189 m).
For glacial phases and associated lake levels, see Hansel et. al., 1985.
Hansel, Ardith K., David M. Mickelson, Allan F. Schneider, and Curtis E. Larsen, 1985. Late Wisconsinan and Holocene history of the Lake Michigan Basin, in Quaternary Evolution of the Great Lakes, P.F. Karrow and P.E. Calkin editors. Geological Association of Canada Special Paper 30. p. 39-53
Photo Detail: Log of the Two Creeks Forest Bed and underlying lacustrine sands.
Caption Credit: John Hoaglund
Photo Credit: John Hoaglund
Photo Date: Friday, May 28, 1999


Two Creeks Forest Bed outcrop bluff with (from bottom) slump slopes obscuring lower till, a lower lacustrine unit, the Two Creeks Forest Bed with logs, an upper lacustrine unit, and upper till. Trenching is required to distinguish lacustrine sands (yellow) from till (red). Note the contact of the upper lacustrine unit with an upper till (car keys for scale) about 2 meters above and to the right (north) of a prominent log.
Photo Detail: View to west of Two Creeks Forest Bed outcrop showing contact between lacustrine sands and upper till.
Caption Credit: John Hoaglund
Photo Credit: John Hoaglund
Photo Date: Friday, May 28, 1999


Close-up of the contact between upper lacustrine sand and upper till. Car keys are stuck in the sand just below the contact. Though minimal trenching is required to expose sedimentologic detail, visitors should respect this outcrop as a "no hammer, shovel, or sampling" outcrop.
Photo Detail: Contact of lacustrine sand with till.
Caption Credit: John Hoaglund
Photo Credit: John Hoaglund
Photo Date: Friday, May 28, 1999


North end of Two Creeks Forest Bed outcrop showing forest bed within slopes.
Photo Detail: View to SW of the north end of the Two Creeks Forest Bed outcrop
Caption Credit: John Hoaglund
Photo Credit: John Hoaglund
Photo Date: Friday, May 28, 1999


In situ upright stump and fallen log (note car keys) mark position of the Two Creeks Forest Bed on sloping north end of outcrop.
Photo Detail: In situ upright stump and fallen log.
Caption Credit: John Hoaglund
Photo Credit: John Hoaglund
Photo Date: Friday, May 28, 1999