Stratigraphy, Provenance, and Tectonic Significance of the Punchbowl Block, San Gabriel Mountains, California, USA GEOSPHERE, V

Home , Barstovian, Clarendonian, Mint Canyon Formation, Orocopia Mountains, Punchbowl Formation, San Francisquito Canyon

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GEOSPHERE Stratigraphy, provenance, and tectonic significance of the Punchbowl block, San Gabriel Mountains, California, USA GEOSPHERE, v. 15, no. 2 Kevin T. Coffey1,2, Raymond V. Ingersoll1, and Axel K. Schmitt1,3 https://doi.org/10.1130/GES02025.1 1Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, California 90095-1567, USA 2Department of Earth Sciences, El Camino College, Torrance, California 90506, USA 3 12 figures; 1 table; 1 set of supplemental files Institute of Earth Sciences, Heidelberg University, Im Neuenheimer Feld 236, 69120 Heidelberg, Germany

CORRESPONDENCE: kevincoffey@ucla.edu ABSTRACT bowl block is generally accepted as an offset equivalent of the Soledad region; CITATION: Coffey, K.T., Ingersoll, R.V., and Schmitt, therefore, its previously understudied strata provide important constraints on A.K., 2019, Stratigraphy, provenance, and tectonic significance of the Punchbowl block, San Gabriel The Punchbowl block is a fault-bounded crustal sliver in the eastern San these palinspastic reconstructions. Furthermore, Oligocene–Miocene strata of Mountains, California, USA: Geosphere, v. 15, no. 2, Gabriel Mountains of southern California with important implications for the Punchbowl block straddle the Fenner fault, a component of a proposed p. 479–501, https://doi.org/10.1130/GES02025.1. conflicting reconstructions of the San Andreas fault system. Detailed map- early trace of the San Andreas fault, the existence of which is debated (e.g., ping, determination of conglomerate-clast and sandstone compositions, Powell, 1981, 1993; Richard, 1993). For these reasons, we conducted a detailed Science Editor: Raymond M. Russo and dating of detrital and igneous zircon of Oligocene–Miocene strata de- study of these strata. Our findings support original alignment of the Tejon, fine two distinct subbasins and document initiation of extension and vol- Soledad, Punchbowl, and Orocopia regions, and the slip estimates implied Received 14 June 2018 Accepted 7 November 2018 canism ca. 25–24 Ma, followed by local exhumation of the Pelona Schist, thereby, and they argue against an early trace of the San Andreas fault system and transition from alluvial-fan to braided-fluvial deposition. Strata of the along the Fenner fault. Published online 16 January 2019 Punchbowl block correlate with those of other regions in southern Califor- nia, confirming 40–50 km of dextral slip on the Punchbowl fault, and sup- porting reconstructions with 60–70 km of dextral slip on the San Gabriel/ N35° Canton fault and ~240 km of dextral slip on the southern San Andreas fault. Simmler basin N Plush Ranch basin

Provenance and probable correlations of Punchbowl-block strata argue Tejon S a Ca n Charlie Canyon subbasin against 80–110 km of dextral slip on the San Francisquito–Fenner–Clemens f lifornia BP/LV G SFf Sierra Pelona a Well fault and limit the time interval during which such slip could have b Texas Canyon subbasin 50 km ri WTR e Vasquez Rocks subbasin occurred. Synthesis of these findings with previous work produces paleo- l/ Ca Soledad Fig. 3 S a n n geographic reconstructions of the Punchbowl block and its probable cor- to figure n f A . Pf n area relatives through time. d r e a Los Angeles s f a u N34° l t Punchbowl SGP block Diligencia basin Pacific Ocean Palm Springs INTRODUCTION Orocopia OLD G Santa Catalina Salton CW /O The Punchbowl block, a crustal sliver between the Punchbowl and San Sea M Island f Andreas faults (Fig. 1; e.g., Dibblee, 1987), contains Oligocene–Miocene strata, the older parts of which had not been thoroughly investigated prior to this W119°WW118° 117° W116° OPEN ACCESS study. Similar Oligocene–Miocene strata are present in the Tejon, Soledad, and Orocopia regions of southern California, which lie on different sides of Figure 1. Regional map showing Punchbowl block (including location of Fig. 3), and Tejon, Sole- dad, and Orocopia regions. Areal extents of Upper Oligocene–Lower Miocene strata in these the San Gabriel/Canton and San Andreas faults (Fig. 1; e.g., Crowell, 1975a). regions are schematically shown in gray, delineating the Simmler, Plush Ranch, and Diligencia Some palinspastic reconstructions show the Tejon, Soledad, and Orocopia re- basins and Charlie Canyon, Texas Canyon, and Vasquez Rocks subbasins of Soledad basin. gions as correlated and originally adjacent to each other (e.g., Hill and Dibblee, Relevant faults also shown. Sierra Pelona, site of paleodrainage divide and anticlinorium of 1953; Crowell, 1962, 1975a; Carman, 1964; Ehlig and Ehlert, 1972; Bohannon, Pelona Schist, is also shown. Abbreviations: f.—fault; BP/LVf—Big Pine/Lockwood Valley fault; CW/OMf—Clemens Well/Orocopia Mountains fault; Pf—Punchbowl fault; SFf—San Francis- This paper is published under the terms of the 1975), whereas others do not correlate some of these regions (e.g., Powell, quito fault; SGP—San Gorgonio Pass; WTR—western Transverse Ranges. Figure is after Frizzell CC‑BY-NC license. 1981, 1993; Spittler and Arthur, 1982; Frizzell et al., 1986). The central Punch- and Weigand (1993) and Law et al. (2001).

GEOLOGIC BACKGROUND North American Oligocene–Miocene Basins Land Tejon Soledad Punchbowl Orocopia Epoc h Mammal region region block region Punchbowl Block Ages Blancan Saugus Fm.

Plio Quatal Fm. ?? The Punchbowl block contains the Punchbowl Formation (Noble, 1953, Lockwood Clay Pico Fm. Hemphilian ?? 1954), ~1500 m of fluvial/alluvial conglomerate, sandstone, and minor mud- Castaic Fm. 10 Punchbowl stone, which accumulated during the middle-late Miocene (Fig. 2; Tedford and Fm. Clarendonian Caliente Mint Canyon Downs, 1965; Woodburne and Golz, 1972; Woodburne, 1975; Dibblee, 1987; Liu, Fm. Fm. basal Punchbowl ?? 1990). A distinct basal member is middle Miocene in age (Noble, 1954; Liu, 1990; iocene Barstovian ??Paradise Springs Tick Canyon fm. personal commun. with Allen and Whistler in Liu, 1990). The older units docu- Age (Ma ) Hemingfordian strata ?? mented in this study (the Paradise Springs and Vasquez formations; Fig. 2) have 20 Diligencia been interpreted in previous studies as either part of the basal Punchbowl For- Plush Ranch Vasquez ??Fm. mation (e.g., Noble, 1954; Dibblee, 2002a, 2002b, 2002c), or deposits in a fault- Fm. Fm. Vasquez Fm. eM ?? bounded sliver along the Punchbowl fault that originated in a separate basin Arikareean (Weldon et al., 1993). 30 Oligocen Whitneyan

Tejon Region Figure 2. Time-stratigraphic chart showing approximate ages of deposition of Oligocene–Mio- cene strata of Punchbowl block, and of Tejon, Soledad, and Orocopia regions, arranged from The oldest nonmarine strata of the Tejon region belong to the Plush Ranch west (left) to east (right). Straight and wavy lines indicate conformable and unconformable Formation (Fig. 2; Carman, 1954, 1964), composed of alluvial and lacustrine relationships, respectively; queried contacts indicate uncertainty in nature of contact. Details are based on data and references discussed in text, and Stirton (1933), Woodburne and Whistler conglomerate, sandstone, siltstone, shale, limestone, and evaporites (Car- (1973), Woodburne (1975), Ensley and Verosub (1982), McDougall (1982), Lander (1985), Frizzell man, 1964; Cole and Stanley, 1995; Hendrix et al., 2010). Interbedded basalt and Weigand (1993), and Coffey (2015). Age ranges of North American Land Mammal Ages are has been dated by whole-rock and plagioclase K-Ar methods as ca. 26–23 Ma from Woodburne (1987) and Alroy (2000). Figure is after Hoyt et al. (2018). (Crowell, 1973; recalculated after Dalrymple, 1979; Frizzell and Weigand, 1993). Northwest of Plush Ranch basin, on the opposite side of Mount Pinos (which includes exposures of Pelona Schist), Oligocene–Miocene strata are generally preserved in three subbasins (Fig. 1; Jahns and Muehlberger, 1954; Muehl- mapped as Simmler Formation (Fig. 1; e.g., Kellogg and Miggins, 2002; Dib- berger, 1958; Hendrix and Ingersoll, 1987). The Vasquez Rocks and Texas Can- blee, 2005a, 2005b, 2006b), but are considered equivalent to the Plush Ranch yon subbasins, south of Sierra Pelona (where Pelona Schist is exposed; Fig. 1), Formation (personal commun. with Hill and Dibblee in Carman, 1964). These are interpreted to have been depositionally distinct but kinematically linked for strata coarsen upward, from mostly sandstone at the base to coarse conglom- most of their history (Bohannon, 1976; Hendrix and Ingersoll, 1987; Hendrix, erate at the top (Dibblee, 2005a, 2005b). 1993; Hendrix et al., 2010). The Vasquez Rocks subbasin contains interbedded Atop the Plush Ranch Formation, in angular unconformity, there is the volcanic rocks, primarily basaltic andesite with some rhyodacite and rhyolite nonmarine Caliente Formation (named by T.W. Dibblee Jr. in Stock, 1947; (Hendrix and Ingersoll, 1987; Frizzell and Weigand, 1993), dated by whole-rock Schwade, 1954), which is composed of fluvial and lacustrine conglomerate, and plagioclase K-Ar methods as ca. 26–23 Ma (Crowell, 1973; Spittler, 1974; sandstone, and mudstone, with minor tuffaceous and limestone beds (Fig. 2; Woodburne, 1975; recalculated after Dalrymple, 1979; Frizzell and Weigand, Carman, 1964; Ehlert, 2003). 1993). Strata of the Charlie Canyon subbasin, north of Sierra Pelona (Fig. 1), coarsen upward, from siltstone and fine sandstone at the base to coarse conglomerate near the top (Sams, 1964; Hendrix and Ingersoll, 1987). Soledad Region Atop the Vasquez Formation, in angular unconformity, there are strata des- ignated as the Tick Canyon Formation by Jahns (1939, 1940; see also Fig. 2 The oldest nonmarine strata of the Soledad region belong to the Vasquez herein). They consist of alluvial, fluvial, and lacustrine conglomerate, sand- Formation (Fig. 2; Sharp, 1935; Jahns and Muehlberger, 1954; Muehlberger, stone, siltstone, and claystone (Jahns, 1940; Woodburne, 1975). These strata 1958), which is dominated by alluvial conglomerate and sandstone (Jahns and are overlain by, and were originally considered part of, the Mint Canyon For- Muehlberger, 1954; Hendrix and Ingersoll, 1987). The Vasquez Formation is mation (Kew, 1923, 1924), but they were subsequently distinguished on the

basis of an inferred disconformity (Jahns, 1940). Subsequent work discounted plutons (1460–1400 Ma) are present throughout southern California and sur- the presence of a disconformity (Ehlert, 1982, 2003; Lander, 1985; Bishop, rounding regions (Anderson and Bender, 1989), including minor exposure in 1990). In this study, we use the term “Tick Canyon strata” to distinguish these the eastern San Gabriel Mountains (Premo et al., 2007; personal commun. with deposits from overlying strata of the Mint Canyon Formation and underlying J. Nourse, 2017 in Hoyt et al., 2018). strata of the Vasquez Formation. The Proterozoic basement of southern California is intruded by numerous, Tick Canyon strata contain an unroofing sequence, culminating up section overlapping Mesozoic plutons (e.g., Ehlig, 1981). In the San Gabriel Mountains, in clasts of Pelona Schist (Ehlert, 1982, 2003; Hendrix, 1993). The Tick Canyon the oldest of these is the compositionally zoned Mount Lowe intrusion, em- strata also contain abundant volcanic clasts, most of which resemble volcanic placed 218–207 Ma (Barth and Wooden, 2006); similar-age plutons are present rocks of the Vasquez Formation (Hendrix, 1993). The Charlie Canyon sub in the southern Mojave region (e.g., Barth et al., 1997). Most plutons in southern basin of the Soledad region also contains an unroofing sequence in the form California are substantially younger than the Mount Lowe intrusion (e.g., Barth of a Pelona Schist–bearing, poorly sorted breccia, stratigraphically above the et al., 1997). In the San Gabriel Mountains, distinct magmatic episodes occurred Vasquez Formation but below the Mint Canyon Formation (e.g., Sams, 1964; 170–149 Ma and 90–75 Ma (e.g., Silver, 1971; May and Walker, 1989; Barth et al., Weber, 1994; Dibblee, 1997; Coffey, 2015). This breccia has previously been 2008), producing quartz diorite to quartz monzonite (e.g., Ehlig, 1981). considered as the basal Mint Canyon Formation (Dibblee, 1997) and a separate The Paleogene San Francisquito Formation is exposed north of Blue Ridge formation (part of the San Francisquito Canyon breccia by Sams, 1964; the in the Punchbowl block (Dibblee, 1967, 1987). It consists of almost entirely Powerhouse breccia-conglomerate by Weber, 1994). In this study, these strata marine shale, mudstone, sandstone, conglomerate, and minor carbonate, are referred to as Tick Canyon strata. both in the Punchbowl block and in its type area in the Soledad region (Dib- The Mint Canyon Formation consists primarily of fluvial, alluvial, and lacus- blee, 1967; Kooser, 1982); coeval marine deposits are present in the Tejon (e.g., trine conglomerate, sandstone, and mudstone (Fig. 2; Kew, 1923, 1924; Ehlert, Kellogg et al., 2008) and Orocopia (Crowell and Susuki, 1959; Advocate et al., 1982, 2003). The Mint Canyon Formation is overlain by the dominantly marine 1988) regions. Castaic Formation (Crowell, 1954), which consists of shale, sandstone, and The gneissic, granitic, and sedimentary rocks of the San Gabriel Moun- minor conglomerate (Crowell, 1954; Ehlert, 1982). The contact between the Mint tains lie within the upper plate of the Vincent thrust (e.g., Ehlig, 1981). The Canyon and Castaic Formations is an angular unconformity in some places, lower plate is composed of Pelona Schist, which is predominantly meta-arkose and it is apparently conformable and gradational in others (Fig. 2; Ehlert, 1982). (Haxel and Dillon, 1978; Ehlig, 1981; Jacobson et al., 2011). This relationship is exposed in a structural window in the southern San Gabriel Mountains. Pelona Schist is also exposed in the core of an anticlinorium along Blue Ridge Orocopia Region in the Punchbowl block (e.g., Dibblee, 1968), and in the core of anticlinoria in the Tejon and Soledad regions (e.g., Ehlig, 1968; Crowell, 1975a). The cor- The only Oligocene–Miocene strata of the Orocopia region belong to the related Orocopia Schist is exposed in an anticlinorium in the Orocopia region nonmarine Diligencia Formation (Fig. 2; Crowell, 1975b), which is composed (e.g., Crowell, 1962; Ehlig, 1968; Haxel and Dillon, 1978; Jacobson et al., 2007; of alluvial, fluvial, and lacustrine conglomerate, sandstone, siltstone, and lime- Ingersoll et al., 2014). stone (Spittler and Arthur, 1982; Law et al., 2001; Ingersoll et al., 2014). It contains interbedded basalt and andesite flows, dated by whole-rock and plagio clase K-Ar methods as ca. 24–21 Ma (Crowell, 1973; Spittler, 1974; recalculated Tectonic Reconstructions of the Southern San Andreas Fault System after Dalrymple, 1979; Frizzell and Weigand, 1993), and andesitic sills and dikes (Spittler and Arthur, 1982; Terres, 1984). The central Punchbowl block has been correlated with the Soledad region, implying 40–50 km of dextral slip on the Punchbowl fault (Dibblee, 1967, 1968; Ehlig, 1968, 1981; Powell, 1993). Correlation has also been suggested between Potential Source Rocks the central Punchbowl block and either the northwestern Orocopia region (Ehlert and Ehlig, 1977; Ehlig and Joseph, 1977) or the northern Little San Ber- The oldest rocks of the San Gabriel and Punchbowl blocks are Paleoprotero nardino Mountains (Ehlig and Joseph, 1977; Matti and Morton, 1993). zoic gneisses, formed 1800–1660 Ma (Silver, 1968; Ehlig, 1981; Barth et al., Correlation of the Tejon, Soledad, and Orocopia regions (Fig. 1) has been 2001; Premo et al., 2007; Nourse and Premo, 2016), which were intruded by a proposed and refined based on similarities in both basement rocks, and sedi- complex of anorthosite, gabbro, syenite, and norite (e.g., Crowell, 1975a; Ehlig, mentary and volcanic strata (e.g., Hill and Dibblee, 1953; Crowell, 1962, 1975a; 1981) ca. 1200 Ma (Barth et al., 1995, 2001). Perturbation of the Paleoprotero Carman, 1964; Ehlig and Ehlert, 1972; Bohannon, 1975; Ehlert, 1982, 2003; zoic gneisses during intrusion produced discordant zircon with 207Pb/206Pb ages Weigand, 1982; Frizzell and Weigand, 1993; Ingersoll et al., 2014; Hoyt et al., of 1760–1300 Ma (Silver et al., 1963; Barth et al., 1995, 2001). “Anorogenic” 2018). Such correlations imply 60–70 km and ~240 km of dextral slip along the

San Gabriel/Canton and San Andreas faults, respectively (e.g., Crowell, 1975a; Stratigraphy Ingersoll et al., 2014). These correlations have been widely accepted, but also challenged by alternate reconstructions (e.g., Smith, 1977; Powell, 1981, 1993; Vasquez Formation Spittler and Arthur, 1982; Frizzell et al., 1986; Matti and Morton, 1993; Weldon et al., 1993), most of which suggest that 80–110 km of dextral slip occurred The stratigraphically lowest nonmarine strata in the study area are compo- along the San Francisquito–Fenner–Clemens Well fault, and only 42 km and sitionally distinct from overlying strata and contain interbedded volcanic rocks. 160–185 km occurred along the San Gabriel/Canton and southern San Andreas Accordingly, we consider them a separate formation, which we refer to as the faults, respectively (e.g., Powell, 1993). Some of the differences among these Vasquez Formation based on probable correlation with the Vasquez Forma- reconstructions may be reconcilable (Darin and Dorsey, 2013). tion of the Soledad region, as discussed below. The Vasquez Formation of the study area is composed primarily of bright-red conglomerate and sandstone. The conglomerate exhibits low degrees of rounding and sorting, a muddy GEOLOGY OF THE PUNCHBOWL BLOCK matrix, and, commonly, reverse grading. South of Blue Ridge, the Vasquez Formation nonconformably overlies granitoid, although the base of the sec- We mapped the study area in the central Punchbowl block at 1:12,000 scale, tion is excised by the Blue Ridge fault along much of its length (Fig. 3). Inter- To view Figure 3 at full size, please visit https:// documented sediment composition via conglomerate-clast counts, sandstone bedded trachyandesite, previously undescribed, is present near the base of doi.org /10 .1130/GES02025 .f3 or access the full- point counts, and U-Pb dating of detrital zircon, and determined ages of igne- the section (Fig. 3), in places capped by thinly bedded tan limestone (too small text article on www.gsapubs.org. ous rocks via U-Pb dating of zircon. to map). North of Blue Ridge, the Vasquez Formation also lies depositionally

GEOLOGIC MAP OF THE CENTRAL PUNCHBOWL BLOCK, EASTERN SAN GABRIEL MOUNTAINS, SOUTHERN CALIFORNIA, USA

Pεsf Pεsf ’ ’ ’ 1 E’ ’ 0’ Pεsf 9 8 24’ 7 1. 6 3’ 5’ 7°5 °25’ 7°4 7°4 ° 7°4 1 °4 °2 7°44’ °22’ °43’ 11 N34 Qa 44 11 11 N34 11 4N Pεsf 117 N34 F’ 11 N34 117 17°42’ Pεsf W W W Mzgr W W 3 58 W117°4 W W KPεps W1 62 Qa D’ Pεsf Qa Qg 52 40 KPεps G’ 35 Mzgr N C’ 61 64 .2 KPεps KPεps H’ 42 Pεsf 72 Pεsf Qt 11 2 Qa Mzgr 4N 47 KPεps PεNv ’ ’ 68 KPεps 4 6 4°21 °25 73 Qa D N3 34 A’ Qg . 4 N Mzgr Pεsf U 71 N 54 d g e f 51 45 70 Pεsf R i a Qg l t 53 Pεsf 64 57 Qt 78 Qa Qa 1 2 l u e u 2 u Pεvv Pεsf 43 38 78 l t B l t 61 f a ? 83 79 I’ 72 68 56 u PεNv e 38 86 a 1 16 g 37

57 42 f Mzgr i d 88 29 A A 79 A 50 54

Pεsf Qg . 34 R Mzgr 82 1 1

1 Pεsf 70 78 28 dz3 Mzgr KPεps e KPεps 1 1

50 1 39 Qa C K C R E E K Qa Pεsf e r 32 PεNv 72 u

Qa 41 Qg 35 55 QaR O R D Qa n Qg 2 19 B l 45 Qg N N

49 N IG 55 n KPεps 55 43 79

Qa Pεsf B PεNv F e 72 42 39 43 PεNvg Pεvv 4 4 4 4

4 37 36 90 77 74 38 Mzgr 50 KPεps

53 1 64 18 34 PεNv Qt PεNv 71 dz1 Qg D D D 43 1.1 21 54 63 21 74

39 60 1 75 Qa PεNv 54 74 KPε?my

R R R 50 N Mzgr 36 65 64 77 ? 4 Mzgr 77 Pεsf 73 60 52 14 44 PεNv 62 71 77 66 KPεps Qg 58 3 84 36 27 S 52 64 PεNvg Npb 3746 B’ 43 37 Qa D 47 4 Pε?gd Qg dz2 39 44 39 F 55 32 55 PεNv 77 66 42 Mzgr 66 53 KPεps l t PεNv Qt N Qt 71 75 75 Pεsf U 67 f a u Qt 41 59 Pεsf 22 66 46 KPε?my 69 73 44 39 64 Pεsf Pεsf 65 g e PεNv 2 66 Qg 67 59 Npb PεNv 33 R i d 57 Qls 2 KPε?my PεNv 65 50 66 PεNvg 32 e 0 6 18 87 65 43 47 43 60 50 48 49 43 82 B l u Mzqdc 31 58 52 31 Mzgr 75 42 40 87 Qg 46 27 79 Qt 64 P u n c

Qg 71 35 74 PεNv 50 l t Qls h b o w l f a u l

40 Np 38 Pεsf l f a u Xgn 25 t KPε?my 43 72 40 36 h b o w Pε?gd 40 49 48 27 84 49 46 R 83 50 dz4 P u n c KPε?my Qg 52 45 78 D 36 D 40 60 Mzqdc Pε?gd KPεps

40 Qa 39 42 U E Mzgr dz5 56 69 Qa 7 72

42 61 NQa 40 41 52 37 Y 68 47 11 Pε?gd 69 73 PεNv

ine A 67 53 Qa dz6 B A 48 KPε?my 45 70 Pε?gd l 11A Qg F KPε?my owl sync 45 47 52 43 1 60 60 Npss Nps Qt 43 86 KPε?my 54 Punchb 69 4N Qoa 23 Nps Nps Qa 52 71 Qls 74 dz7 55 Qg 68 D 85 83 62 V KPε?my 68 74 50 59 74 70 57 dz8 Xgn 61 32 in 71 72 ’ 51 61 U 82 ? 79 67 32 48 50 Mzqdc ce Pε?gd 26 Pε?gd 47 76 28 65 52 Qoa E 53 nt 34 Pε?gd 7°42 71 35 78 53 Qt Npb 52 Qt 45 1 35 84 Mzgr Xgn Xgn th 40 W1 39 81 62 Pεsf dz10 Mzqdc r 80 KPεps 68 75 86 52 2 u KPεps Pεsf 80 Qt s 12 69 Pεsf Mzgr 74 79 Np Np 39 ’ ’ t 11 ’ ’ 59 67 8’ D 3’ 6 23 4 1’ 43 28 Qg 70 Qa 71 °4 °2 °47’ °4 °22’ °45 °4 KPεps °2 ° 88 87 Qoa 70 73 Mzqdc Mzqdc 117 34 117 117 34 117 29 117 34 117 I 88 75 Pεsf 48 75 57 Qa Qg Qt W N W W N W G W N W Qg 44 76 H Qg 79 62 72 Np 71 C 86 50 45 68 50 67 64 57 Npb 69 61 60 Nps 64 76 9’ 70 74 53 87 7°4 GEOLOGIC SYMBOLS Map Location: TRUE SCALE 1:12000 USGS basemap road classification: USGS basemap data sources: 54 71 66 81 Qt Mzqdc 11 55 Npb Qt W STRIKE AND DIP OF SEDIMENTARY BEDDING: FAULT: NORTH State Route 81 Np t 72 41 58 u l long-dashed where approximately located, short-dashed ANTICLINE OR ANTIFORM: 1 0.5 0 kilometers 1 2 Np 48 Np 56 a 87 Local Road l f 53 long-dashed where approximately located, short-dashed 2017 MAGNETIC NORTH Geodetic reference system: Qg h b o w Mzqdc 26 where inferred, dotted where concealed by surficial sediment; Mescal 39 P u n c B short, solid arrow and number indicate dip of the fault; long, where inferred, dotted where concealed by surficial sediment; N Valyermo +12.0°; changing by -0.1°/yr meters 4-Wheel Drive North American Datum of 1983 (NAD83) inclined overturned vertical arrow and number indicate trend and plunge, respectively, of fold axis. Creek 1000 500 0 1000 2000 46 a u l t Mzqdc open arrow and number indicate trend and plunge, respectively, Cali State Forest Service b o w l f LOCATION OF DETRITAL- map u n c h of slickenlines; perpendicular line and “90” indicate a vertical fault; UTM GRID NORTH 10.5 0 1 Route Primary Route 66 P STRIKE AND DIP OF OTHER PLANAR FEATURES: forni a Roads: ©2006-2011 TomTom ZIRCON SAMPLE: parallel arrows indicate inferred relative lateral movement; 32 rea -0.4° (UTM Zone 11S) Mzqdc Qoa miles Roads within US Forest Service Lands: FSTopo Data 82 “D” and “U” symbols indicate inferred relative dip-slip movement where a 0’ dz7 38 65 SYNCLINE OR SYNFORM: Names: GNIS, 2011 ’ °5 Geology mapped by Kevin T. Coffey, fault type is unknown (D = downthrown side, U = upthrown side); Crystal Mount San 1 Mzqdc foliation schistosity joint long-dashed where approximately located, short-dashed Hydrography: National Hydrography Dataset, 2010 °5 ’ 117 2012 August - 2017 May solid teeth indicate a thrust fault, and point toward the hanging wall. Lake Antonio Contour interval is 40 feet (approximately 12.2 meters) Forest Service Forest Service 117 4 W where inferred, dotted where concealed by surficial sediment; Contours: National Elevation Dataset, 2000 W 4°2 Mzqdc Datum is North American Vertical Datum of 1988 (NAVD88) 3 51 Declination from NOAA National Geophysical Data Center, Passenger Route High-Clearance Route Boundaries: Census, IBWC, IBC, USGS, 1972-2010 Qoa N A CONTACT: 18 D arrow and number indicate trend and plunge, respectively, of fold axis. Cross sections in Figure 4 long-dashed where approximately located, short-dashed calculated 2017 September using the World Magnetic Model (WMM) U 7.5’ quadrangles Basemap is a composite of parts of USGS US Topo 2012 Valyermo, Mescal Creek, Crystal Lake and Mount San Antonio 7.5’ quadrangles where inferred, dotted where concealed by surficial sediment. 90 29 LEGEND Qg - active-stream-channel deposits: Gravel and sand. Y Qg Qa Qls Qt Qa - alluvial-fan deposits: Gravel, sand and mud. Qls - landslide deposits: Coherent slumps (only mapped where obscuring a contact). - UNCONFORMITY - Qt - talus: Loose, angular gravel (only mapped where obscuring a contact). ERNAR Qoa Older alluvium: Inactive, uplifted, unconsolidated deposits of alluvial gravel and sand. QU AT - UNCONFORMITY - Punchbowl Formation (of Noble, 1953, 1954); middle to upper Miocene, non-marine Np Np: Gray to white to tan conglomerate, arkosic sandstone and minor mudrock, containing clasts of gneiss, granitoid, sandstone from the San Francisquito Fm. (Pεsf), andesite and Pelona Schist (KPεps). Npb - basal member: Pink to red to buff conglomerate and sandstone, containing clasts of gneiss, granitoid, Pelona Schist Npb (KPεps) and sandstone from the San Francisquito Fm. (Pεsf). Transitions into Np; definition of upper boundary somewhat arbitrary.

Paradise Springs formation (parts of various units of Punchbowl Formation of Dibblee, 2002a,b,c); middle Miocene, non-marine Nps Nps: Bright red conglomerate and sandstone, clasts dominated by sandstone from the San Francisquito Fm. (Pεsf), with minor amounts of volcanics (Pεvv), gneiss and, in the upper section, Pelona Schist (KPεps). NEOGENE Npss Npss - schist breccia: Very poorly sorted breccia of 100% Pelona Schist (KPεps) clasts, with deep maroon sandstone matrix.

Vasquez Formation (“Tprc” unit of Punchbowl Fm. of Dibblee, 2002a,b,c); upper Oligocene to lower Miocene, non-marine PεNv: Bright red conglomerate and very coarse to very fine sandstone, with minor siltstone and lacustrine carbonate. Conglomerate contains clasts of granitoid (Mzgr), volcanics (Pεvv) and sandstone and conglomerate intraclasts. Near Paradise Springs, some clasts of PεNv sandstone from the San Francisquito Fm. (Pεsf) are present. No clasts of schist present. Highly metasomatized in easternmost exposure. Pεvv Pε?gd Pεvv - volcanics: Trachyandesite flows, interbedded with lower PεNv, containing abundant, cm-scale plagioclase laths. Fractured, and locally brecciated, with tan carbonate filling fractures and cementing the breccia. Locally contains entrained clasts of PεNv. A Figure 3. Geologic map of central Punchbowl block. Note distinct units of Oligocene–Miocene strata both north and south of Blue Ridge, along which an anticlinorium of Pelona Schist is exposed. PεNvg porphyritic rhyolite present as clasts in nearby conglomerate is presumably closely related, but is not found as outcrop. PεNvg - granitoid breccia: White, very poorly sorted breccia of 100% quartz monzodiorite (Mzgr) clasts, with only minor maroon sandstone matrix. Location is shown in Figure 1, cross sections are in Figure 4, and schematic stratigraphic columns are given in Figure 5. UTM—Universal Transverse Mercator; NOAA—National Oceanic and Atmo- Pε?gd: White to tan, very fine-grained, leucocratic hypabyssal intrusive. Complexly intruded into Pelona Schist (KPεps) and mylonite LEOGENE (KPε?my), commonly parallel to schistosity and foliation. spheric Administration; USGS—U.S. Geological Survey. To view Figure 3 at full size, please visit https://doi.org/10.1130/GES02025.f3 or access the full-text article on www.gsapubs.org. PA - UNCONFORMITY - San Francisquito Formation (of Dibblee, 1967; Martinez Formation of Noble, 1954); Paleocene to Eocene, marine Pεsf Clay shale, dark brown to gray, well bedded, poorly exposed, with interbedded, more resistant tan sandstone and minor conglomerate. - UNCONFORMITY - Dark-gray mylonite with white feldspar augen. Foliation variably developed. Emplaced structurally above the Pelona Schist (KPεps) KPε?my along the Vincent thrust. Complexly intruded by Pε?gd.

Pelona Schist, dominantly meta-arkose; Late Cretaceous to Paleogene Gray to brown, fine-to-coarse-grained mica schist, composed of mica, quartz and plagioclase, with minor quartz veins. KPεps Schistosity generally strong but locally weak. Schistosity commonly tightly folded. Locally fractured and altered in eastern part of map area near faulted contact with Nv. Complexly intruded by Pε?gd.

Wilson Diorite (of Miller, 1934) Complex of gray to black quartz diorite intruded into gneiss. Quartz diorite is fine-to-coarse-grained, Mzqdc massive to gneissoid, and consists of plagioclase, biotite, hornblende, and minor quartz and potassium feldspar. Locally highly fractured, especially along the Punchbowl fault, and locally complexly intruded by aplite. MESOZOIC Mzgr White to tan to gray, fine-to-medium-grained intrusive, containing quartz, potassium feldspar, plagioclase, variable amounts of biotite, and, locally, minor hornblende. Composition varies from granite to quartz monzonite to granodiorite to quartz monzodiorite.

White-and-black banded, well foliated gneiss, composed of quartz, feldspar and biotite. Locally includes a coarse-grained, hornblende- Xgn rich amphibolite. Highly fractured. Locally cataclastic along the Vincent thrust. LEOPRO - TEROZOIC PA

atop granitoid, possibly with some intervening San Francisquito Formation in is typically well sorted and subrounded to rounded, with sandy matrix. Chan- places (Fig. 3). The Vasquez Formation north of Blue Ridge contains lenses of nels are abundant and exhibit normal grading. We recognized basal strata of very poorly sorted, very angular, matrix-poor megabreccias (map unit PεNvg the Punchbowl Formation as a distinct member (Fig. 3). This basal member is in Figs. 3 and 4) interbedded with Vasquez Formation conglomerate and sand- composed of pink to red to buff conglomerate and sandstone. It is texturally stone. These deposits fit the definitions of “crackle breccia facies” and “jigsaw intermediate between the overlying main member of the Punchbowl Forma- breccia facies” (i.e., Yarnold and Lombard, 1989, p. 12). tion and the underlying Paradise Springs formation, though more similar to The sorting, rounding, grading, and matrix within Vasquez conglomerate the former. The contact between the basal and main members of the Punch- suggest deposition by debris-flow and hyperconcentrated-flow mechanisms bowl Formation is transitional. (e.g., Blackwelder, 1928; Fisher, 1971). We interpret the Vasquez Formation to The Punchbowl Formation has been interpreted as dominantly fluvial (e.g., represent primarily proximal alluvial-fan deposits. Using the criteria of Yar- Dibblee, 1987). The basal Punchbowl Formation’s intermediate texture and nold and Lombard (1989) and Yarnold (1993), we interpret lenses of granitoid color compared to the Paradise Springs and Punchbowl formations suggest crackle and jigsaw breccia in the Vasquez Formation north of Blue Ridge as that it represents the transition from alluvial to fluvial deposition. rock-avalanche deposits. We interpret the thin interval of thinly bedded lime-

TABLE S1. IGNEOUS-ZIRCON AGE DATA Samples KTC-13-and3 and KTC-14-and4 (combined) n = 28 Latitude/Longitude (WGS84):Sample KTC-13-and3: N34.38050§†† W117.77122§†† stone atop the interbedded trachyandesite as lacustrine, likely the result of Sample KTC-14-and4: N34.35614 W117.71792 (%)correlation Age (Ma) Age (Ma) Age (Ma) Preferred Sediment Composition + 94 + 206 207 207 206 207 207 UO / Zr2O UThRadiogenic Pb*/ ± Pb*/ ± Pb*/ ±of concordia Pb/ ± Pb/ ± Pb/ ±age ± Analysis Number U+ (cps)(ppm) (ppm) 206Pb 238U (1σ) 235U (1σ) 206Pb* (1σ) ellipses 238U (1σ) 235U (1σ) 206Pb (1σ) (Ma) (1σ) 2014_08_08Aug\ [email protected] 88.4 100 0.0037 0.0002 0.0304 0.0023 0.0594 0.0036 0.63323.91.4430.52.3 582132 23.91.44 ponding against the volcanic flows. 2014_08_08Aug\ [email protected] 8.59 1870 155 64.699.70.03520.00250.250.02410.0515 0.0025 0.882223 15.4 22619.6263 110223 15.4 2014_08_08Aug\ [email protected] 8.6178035.8 26.699.90.194 0.0192.170.243 0.0812 0.0031 0.944 1140103 117077.91230 74.4 1230 74.4 2014_08_08Aug\ [email protected] 8.58 1740 98.6 53.399.80.196 0.0183 2.12 0.207 0.0784 0.0016 0.98 115098.7 115067.41160 39.1 1160 39.1 2014_08_08Aug\ [email protected] 8.82 2030 189 113 99.9 0.0336 0.0017 0.2330.01420.0503 0.0016 0.853213 10.9 21211.7208 74.1 213 10.9 2014_08_08Aug\ [email protected] 8.85 2040 270 93.8990.00370.00020.02250.00420.0438 0.0073 0.49 23.9 1.46 22.5 4.17 b.d. b.d. 23.91.46 2014_08_08Aug\ [email protected] 8.49 1920 30.5 18.699.80.220.02272.450.270.0806 0.0024 0.965 1280120 126079.61210 57.4 1210 57.4 The high relative abundance of trachyandesite and rhyolite clasts imme- 2014_08_08Aug\ [email protected] 8.74 1910 91.6 107 99.8 0.1870.01362.070.147 0.0803 0.0010.986 110073.6 114048.81200 23.7 1200 23.7 Conglomerate-Clast Composition 2014_08_08Aug\ [email protected] 8.73 1950 23.8 10.299.80.190.01892.120.194 0.0809 0.0023 0.959 1120102 116063.21220 55.8 1220 55.8 2014_08_08Aug\ [email protected] 8.82 2060 861 382 99.9 0.2760.01273.910.179 0.103 0.0004 0.996 157064.3 1620371680 7.24 16807.24 2014_08_08Aug\ [email protected] 88.899.70.263 0.0182 3.66 0.256 0.101 0.0008 0.994 151092.9 156055.81640 14.1 1640 14.1 2014_08_08Aug\ [email protected] 86.999.90.237 0.0113.220.149 0.0985 0.0008 0.983 137057.3 146035.81600 15.8 1600 15.8 2014_08_08Aug\ [email protected] 184 99.7 0.0253 0.0017 0.1630.01420.0466 0.0026 0.775161 10.4 15312.429.2132 161 10.4 diately up section of the trachyandesite flows (see below) suggests that the 2014_08_08Aug\ [email protected] 0.0089 1.83 0.104 0.0786 0.0015 0.943 101049.2 106037.21160 37.4 1160 37.4 2014_08_08Aug\ [email protected] 17.2 100 0.17 0.0147 1.82 0.174 0.0777 0.0020.966 101081 105062.61140 50.6 1140 50.6 2014_08_08Aug\ [email protected] 75.599.80.192 0.0136 2.15 0.155 0.081 0.0012 0.98 113073.5 116049.91220 28.4 1220 28.4 2014_08_08Aug\ [email protected] 67.999.80.203 0.0131 2.21 0.15 0.0791 0.0012 0.977 119070.4 119047.61170 28.9 1170 28.9 2014_08_08Aug\ [email protected] 2060 53.3 29.299.90.197 0.0173 2.15 0.234 0.079 0.0023 0.98 116093 117075.41170 57.4 1170 57.4 2014_08_08Aug\ [email protected] 90.199.60.266 0.0143 3.67 0.197 0.10.00080.989 152073 157042.91630 14.6 1630 14.6 rhyolite clasts are from deposits closely related to, and thus broadly coeval Conglomerate-clast composition was determined at locations across the 2014_08_08Aug\ [email protected] 8.46 1870 164 96.599.80.221 0.0149 2.48 0.172 0.0813 0.0012 0.978 129078.4 127050.11230 28.6 1230 28.6 2014_08_08Aug\ [email protected] 100 0.2090.02492.460.287 0.0852 0.0026 0.966 1230133 126084.31320 60.1 1320 60.1 2014_08_08Aug\ [email protected] 8.61940891 20.499.90.301 0.0174.270.245 0.103 0.0005 0.996 170084 169047.31680 9.26 16809.26 2014_08_08Aug\ [email protected] 8.73 2010 613 116099.90.02310.00120.156 0.0101 0.0491 0.0014 0.9147 7.83 1478.86154 66.7 1477.83 2014_08_08Aug\ [email protected] 8.64 2020 575 198 99.8 0.0371 0.0021 0.2490.01560.0487 0.0013 0.902235 13.1 22612.7132 63.6 235 13.1 2014_08_08Aug\ [email protected] 8.72030509 164 99.9 0.2990.01594.390.230.107 0.0004 0.998 169078.9 171043.41740 6.92 17406.92 with, the trachyandesite flows. If so, then the 24.4 ± 0.9 Ma age we determined study area. A flexible grid was affixed to conglomeratic beds, and the lithology 2014_08_08Aug\ [email protected] 8.72070108 35.597.20.00420.00030.02630.01110.046 0.0182 0.39926.72.2326.311b.d.b.d. 26.72.23 2014_08_08Aug\ [email protected] 8.79 2070 239 193 99.9 0.2790.01684.020.236 0.104 0.0009 0.99 159084.5 164047.71700 15.3 1700 15.3 2014_08_08Aug\ [email protected] 8.72030183 102 99.8 0.1990.01312.170.144 0.0794 0.0009 0.985 117070.7 117046.21180 22.7 1180 22.7 Summary statistics for the 3 youngest ages (interpreted as magmatic age): Final age: 24.4 ± 0.9 Ma 1σ 1 MSWD = 0.65 for the rhyolite clasts (Table S1 in the Supplemental Files ) should approximate of the clast at each crosshair was determined until 100 counts were reached; Probability = 0.52 the age of the trachyandesite flows, and thus the age of the interbedded strata. grid spacing was varied between locations such that it always exceeded the 1Supplemental Files. Table S1: Igneous-zircon data Therefore, deposition of the Vasquez Formation in the Punchbowl block prob- average clast size. and methods. Table S2: Conglomerate-clast-count data and lithologic descriptions. Table S3: Raw and ably began ca. 25–24 Ma or earlier. Conglomerate-clast composition data are shown in Figure 5 (raw data recalculated sandstone point-count data. Table S4: are in Table S2 [see footnote 1]). Clasts of Pelona Schist are only present in Detrital-zircon data. Please visit https://doi.org/10 the upper part of the Miocene strata (the Paradise Springs and Punchbowl .1130/GES02025.S1 or access the full-text article on Paradise Springs Formation www.gsapubs.org to view the Supplemental Files. formations). Throughout the study area, granitoid makes up the majority Overlying the Vasquez Formation, there are compositionally distinct of the conglomerate-clast population of the Vasquez Formation. Adjacent strata here informally dubbed the “Paradise Springs formation.” The Para to and immediately up section from the interbedded trachyandesite flows, dise Springs formation is texturally similar to the Vasquez Formation: It is trachyandesite and rhyolite clasts make up 30%–39% of the conglomerate composed of bright-red conglomerate and sandstone, with the conglomerate clasts; the more stable rhyolite clasts are found in low abundance through- exhibiting low to moderate degrees of rounding and sorting, and a sandy out most of the section. The Paradise Springs formation conglomerate is to muddy matrix. The Paradise Springs formation is present both north and dominated by sandstone clasts derived from the San Francisquito Forma- south of Blue Ridge; in both cases, basal strata and the contact with the tion; south of Blue Ridge, granitoid clasts are also abundant. Pelona Schist Vasquez Formation are covered by Quaternary deposits (Fig. 3). South of Blue clasts are absent in the lower part of the Paradise Springs formation, but Ridge, along the Blue Ridge fault, there is a spatially restricted breccia (map they constitute up to 7% of the conglomerate clasts higher in the section; the unit Npss in Fig. 3). This breccia is very angular and very poorly sorted, with spatially restricted breccia unit is composed entirely of Pelona Schist clasts. a deep-maroon sandy matrix. The Punchbowl Formation, including the basal member, is dominated by We interpret the Paradise Springs formation to represent alluvial-fan de- granitoid and gneiss clasts; clasts of sandstone from the San Francisquito posits. The textural differences compared to the Vasquez Formation suggest Formation are present, but they are much less abundant than in the underly- less proximal deposition, except for the breccia unit. ing Paradise Springs formation.

Punchbowl Formation Sandstone Composition

North of Blue Ridge, the Paradise Springs formation is overlain by the Sandstone composition was determined for samples collected through- Punchbowl Formation (Noble, 1953, 1954), with no discernible angular dis- out the study area. Sandstone samples were mounted as standard 30-μm- cordance (Fig. 3). The main member of the Punchbowl Formation is gray to thick thin sections by R.A. Petrographic and then etched with concentrated white to tan conglomerate, sandstone, and minor mudrock. The conglomerate hydrofluoric acid (HF) and stained with a saturated solution of sodium

A 199° no vertical exaggeration 19° A′ CC214° no vertical exaggeration 34° ′ 1800 183° no vertical exaggeration 3° 2000 Qoa B B′ Punchbowl Qoa Mzqdc Punchbowl fault fault 1600 Npb 1600 1800 Mzqdc Mzqdc Npb Qg Qg

Qt Mzqdc Np Qa 1400 1600 Np t 1400 l Qa Qg

P u

u a f Pεsf Np

n l Npb c elevation (m) w

h 1200 o

b Np b elevation (m) 1200 Mzgr 1400 Nps o h w c Pεsf ? Pεsf elevation (m)

l n Pεsf f u ? Pεsf a Pεsf P u

1000 l

t 1200 1000

Punchbowl faul 0200 400600 800100012001400 1600 1800 2000 Mzgr Mzgr distance (m) 0200 400600 8001000 1200 ? distance (m) 1000 Fenneroriginal fault? DD205° no vertical exaggeration 25° ′ 800 2200 EE192° no vertical exaggeration 12° ′ t KPεps ? 2200 0200 400600 80010001200 Punchbowl distance (m) 2000 fault Mzqdc lt 2000 u a FF259° no vertical exaggeration 79° ′ PεNv f 2400 Punchbowl f. PεNv e PεNvg g d Fenner f. 1800 i Punchbowl f. R Mzgr 1800 e Qt Qa lu Qg B 2200

F t l 1600 e Qg Xgn u n Nps a f n KPεps 1600 e elevation (m) lt Mzqdc e Xgn r 2000

g au

f f Pεsf PεNv d . i e g R id 1400 R e KPε?my Qg Mzgr ue u Mzgr Bl l Pεsf 1400 B KPεps

1800

? ? KPεps elevation (m) KPεps

1200 P elevation (m)

Punchbowl faul ? or u igi 1200 n na c l F 0200 400600 800100012001400 1600 KPεps h ? en b ) ne distance (m) o r w 1000 fa u l l t? f . 1400 KPεps 0200 400600 800100012001400 1600

t ? 800 (reactivated? distance (m) Fenner fault HH246° no vertical exaggeration 66° ′ 2200 600 II237° no vertical exaggeration 57° ′ ? Mzgr PεNv 2200 Punchbowl 2000 fault 400 Pε?gd KPε?my 0200 400600 80010001200 Pεvv distance (m) 2000 PεNv 1800 Mzgr

t GG237° no vertical exaggeration 57° ′ l t n t PεNv u 1800 hr ce l fa u 2200 u a Mzgr Punchbowl fault e s n f KPε?my g Xgn Punchbowl 1600 id t t PεNv R e fault Qg ue Qg g Bl id lt 1600 R u elevation (m) 2000 fa e KPε?my Pε?gd u e 1400 l g B d KPεps i R Qg e elevation (m) 1400 V lu KPεps 1800 i B KPεps n c 1200 en KPεps KPε?my t t KPε?my Qg hr us 1200 1600 t elevation (m) KPεps 0200 400600 80010001200 1000 Vi n distance (m) KPεps thrust cent Pε?gd KPεps 1400 Pε?gd 800 Figure 4. Cross sections along section lines of Figure 3. No vertical KPεps exaggeration. Map unit abbreviations are given in Figure 3. 1200 0200 400600 800100012001400 0 200400 600800 1000 1200 1400 1600 distance (m) distance (m)

A south of Blue Ridge B north of Blue Ridge

N = 1; n = 100 Punchbowl fault N = 1; N = 1; 800 n = 100 n = 100 800 Paradise Springs formation Punchbowl Formation (Nps): cgl. & ss. N = 1; schist breccia of (Np): cgl. & ss. Paradise Springs n = 100 600 formation (Npss) 600 N = 2; unconformity? n = 200 basal Punchbowl Formation (Npb): N = 2; 400 cgl. & ss. Paradise Springs formation n = 200

meters 400 fault

meters (Nps): cgl. & ss. rhyolite conglomerate Vasquez Formation clasts: 24.4 ± 0.9 Ma (PεNv): cgl. & ss. N = 2; unconformity? y 200 n = 200 200 Vasquez Formation N = 1; trachyandesite (Pεvv) (PεNv): cgl. & ss. n = 100 angularonformit

unc granitoid breccia of 0 Blue Ridge N = 2; granitoid breccia of Vasquez Formation 0 n = 200 fault? Vasquez Formation granitoid (Mzgr) (PεNvg) granitoid (Mzgr) N = 1; (PεNvg) 146 ± 3 Ma n = 100 nonconformity nonconformities N = 1; n = 100 San Francisquito Formation (Pεsf): shale, ss. & fine cgl. N = 1; n = 100

conglomerate-clast composition key

San Francisquito intermediate volcanic felsic volcanic reworked Vasquez unknown & Pelona Schist gneiss granitoid other intrusive Formation ss. & cgl. rocks (e.g., trachyandesite) rocks (e.g., rhyolite) Formation ss. unidentifiable

Figure 5. Schematic composite stratigraphic sections of Oligocene–Miocene strata (A) south and (B) north of Blue Ridge in Punchbowl block. Units, unit symbols (e.g., Nps), and unit colors are same as in Figures 3 and 4; more detailed lithologic descriptions of units are given in text and Figure 3. Paradise Springs formation and upper Vasquez Formation occur on both sides of Blue Ridge, whereas lower Vasquez Formation is only present south of Blue Ridge, and Punchbowl Formation is only north of Blue Ridge. Conglomerate-clast compositions are shown at approximate stratigraphic positions at which they were measured (measurements at similar stratigraphic positions have been combined; raw data, locations, and details of clast lithologies are given in in Table S2 [text footnote 1]). Note differences in composition between units, and occurrence of Pelona Schist clasts up section in both columns. Stratigraphic thicknesses were estimated using Figure 3. N—number of measurement locations; n—total number of clasts counted; cgl.—conglomerate; ss.—sandstone.

hexanitrocobaltate (III) (Na3Co[NO2]6). Etching and staining distinguish grid spacing was greater than the average grain size. Categories of framework quartz (unetched; unstained), potassium feldspar (stained with yellow dots), grains (>0.0625 mm) are defined in Table 1; points interstitial to framework and plagioclase feldspar (heavily etched; unstained; Gabriel and Cox, 1929; grains were also counted. Where diagenetic alteration had occurred, frame- Reeder and McAllister, 1957; Ingersoll and Cavazza, 1991). For each thin sec- work grains were counted as their original grain type. Point counts were also tion, 400–500 points were analyzed using the Gazzi-Dickinson method of point performed on samples collected and prepared by others in the same manner; counting (Gazzi, 1966; Dickinson, 1970; Ingersoll et al., 1984). For each sample, details are given in Table S3 (see footnote 1).

TABLE 1. DEFINITION OF ORIGINAL AND RECALCULATED SANDSTONE POINT-COUNT GRAIN CATEGORIES CategorySymbol Description Original categories Quartz, monocrystalline Qm Quartz crystal with a maximum diameter >0.0625 mm Quartz, polycrystalline Qp Interlocking quartz crystals with maximum diameters <0.0625 mm; no other associated mineral phases Feldspar, plagioclase Fp Plagioclase-feldspar crystal with a maximum diameter >0.0625 mm Feldspar, potassium Fk Potassium-feldspar crystal with a maximum diameter >0.0625 mm Mica, monocrystalline MMica (or chlorite) crystal with a maximum diameter >0.0625 mm Dense mineral, monocrystalline DCrystal of any mineral phase not listed above with a maximum diameter >0.0625 mm Lithic fragment, metamorphic, aggregateLma Interlocking crystals with maximum diameters <0.0625 mm and little or no preferred orientation (typically quartz, feldspar, and/or micas) Lithic fragment, metamorphic, tectoniteLmt Interlocking crystals with maximum diameters <0.0625 mm and distinct preferred orientation (typically quartz, feldspar, and/or micas) Lithic fragment, metamorphic, micaceous LmmInterlocking crystals of mica with maximum diameters <0.0625 mm; no other associated mineral phases Lithic fragment, metamorphic, metavolcanic LmvInterlocking crystals with maximum diameters <0.0625 mm recrystallized from a volcanic rock (commonly plagioclase and chlorite) Lithic fragment, volcanic, lathwork LvlFragment of volcanic rock containing plagioclase laths Lithic fragment, volcanic, microlitic LvmFragment of volcanic rock with groundmass containing plagioclase microlites Lithic fragment, volcanic, felsitic, seriateLvfsFragment of volcanic rock with groundmass of variable crystal size Lithic fragment, volcanic, felsitic, granular Lvfg Fragment of volcanic rock with equigranular, microcrystalline groundmass Lithic fragment, volcanic, vitric LvvFragment of glassy volcanic rock Lithic fragment, sedimentary, siliciclastic LssFragment of mudrock, i.e., grains have maximum diameters <0.0625 mm (siltstone, shale, mudstone) Lithic fragment, sedimentary, carbonateLsc Fragment of clastic or chemical sedimentary rock of dominantly carbonate composition and grain/ crystal size <0.0625 mm Miscellaneous and unknownM/U Any sand-sized grain that does not fall within one of the above categories or that could not be confidently identified Interstitial material Int. Interstitial material: cement, primary pore space, and detrital grains with maximum diameters <0.0625 mm Recalculated categories Symbol Relationship to original categories Total quartzQ Q = Qm + Qp Total feldspar FF = Fk + Fp Total (nonquartzose) lithics LL = Lma + Lmt + Lmm + Lmv + Lvm +Lvl +Lvfg +Lvfs + Lvv +Lss + Lsc Total metamorphic lithics Lm Lm = Lma + Lmt + Lmm + Lmv Total volcanic lithics Lv Lv = Lvm + Lvl + Lvfg + Lvfs + Lvv Total (nonquartzose) sedimentary lithics Ls Ls = Lss + Lsc Percent total quartz QFL%Q 100% ∙ Q/(Q + F + L) Percent total feldspar QFL%F 100% ∙ F/(Q + F + L) Percent total lithics QFL%L 100% ∙ L/(Q + F + L) Percent monocrystalline quartz QmFkFp%Qm100% ∙ Qm/(Qm + Fk + Fp) Percent potassium feldspar QmFkFp%Fk100% ∙ Fk/(Qm + Fk + Fp) Percent plagioclase feldspar QmFkFp%Fp100% ∙ Fp/(Qm + Fk + Fp) Percent metamorphic lithics LmLvLs%Lm 100% ∙ Lm/(Lm + Lv + Ls) Percent volcanic lithics LmLvLs%Lv100% ∙ Lv/(Lm + Lv + Ls) Percent sedimentary lithics LmLvLs%Ls100% ∙ Ls/(Lm + Lv + Ls)

Most of the Punchbowl block Oligocene–Miocene strata show considerable Detrital-Zircon Ages variation in sandstone composition (Fig. 6). Sandstone from the main member of the Punchbowl Formation, however, clusters very tightly on total quartz– Nine >1 kg sandstone samples were collected for detrital-zircon analysis total feldspar–total (nonquartzose) lithics (QFL) and monocrystalline quartz– (Fig. 3). Samples were crushed and sieved and then separated by density and potassium feldspar–plagioclase feldspar (QmFkFp) ternary diagrams; the large magnetism using: (1) a Mineral Technologies MD Gemini shaking table at spread on the metamorphic-volcanic-sedimentary lithic (LmLvLs) ternary dia Pomona College or tetrabromoethane (ρ = 2.97 g/cm3), (2) a neodymium hand gram is presumably caused by the extremely low abundance of lithic grains magnet and a model L-1 Frantz isodynamic magnetic separator, and (3) methy (grain categories are defined in Table 1; Hoyt et al., 2018). Sandstone from the lene iodide (ρ = 3.32 g/cm3). At the Arizona LaserChron Center at the Univer- basal Punchbowl Formation shows more variation than the overlying main sity of Arizona, large splits of these separates were mounted, together with Punchbowl Formation but less variation than the underlying Vasquez and Para grains of zircon references, on epoxy plugs, which were polished to a depth of dise Springs formations (Fig. 6). The Vasquez Formation, which is dominated ~20 μm to expose crystal interiors. by granitoid and volcanic conglomerate clasts, is dominated by feldspar, espe- Detrital zircon was dated by U-Pb methods using laser-ablation–multicol- cially plagioclase, in the sandstone fraction. The Paradise Springs formation, lector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS) at the which is dominated by sandstone conglomerate clasts from the San Francis- Arizona LaserChron Center, using protocols described by Gehrels et al. (2006, quito Formation, contains significantly more quartz and sedimentary lithics in 2008). Material was ablated using a Photon Machines Analyte G2 excimer the sandstone fraction. laser and then carried in helium into the plasma source of a Nu high-resolution ICP-MS. A 204Pb-based common Pb correction was performed, using the common Pb composition from Stacey and Kramers (1975). U/Pb, Th/U, and Q Pb-isotope relative sensitivities were determined using zircon reference Sri NORTH OF BLUE RIDGE: SOUTH OF BLUE RIDGE: Lanka (563.5 ± 1.6 Ma; ~518 ppm U and 68 ppm Th; Gehrels et al., 2008). The Punchbowl Fm. (Np) Paradise Springs fm. (Nps) accuracy of final ages was verified using zircon reference R33 (419.3 ± 0.4 Ma; Basal Punchbowl Fm. (Npb) Schist breccia of Paradise Black et al., 2004). Analytical data are reported in Table S4 (see footnote 1). Springs Fm. (Npss) Additional details of preparation and analysis were given in Coffey (2015). Paradise Springs fm. (Nps) Vasquez Fm. (PεNv) Relative-probability distributions of detrital-zircon ages are given in Figure 7 Vasquez Fm. (PεNv) (raw data are in Table S4 [footnote 1]). Distributions for all samples south of Granitoid (Mzgr: outcrop Blue Ridge (Fig. 7A) are dominated by peaks at ca. 1200 Ma and 1660–1800 Ma, Granitoid breccia of and conglomerate clast) and they exhibit low, broad peaks at ca. 1400 Ma. Distributions for all samples Vasquez Fm. (PεNvg) north of Blue Ridge (Fig. 7B) lack ca. 1200 Ma peaks and exhibit smaller peaks F L at ca. 1400 Ma and 1660–1800 Ma. Many samples contain peaks at ca. 150 Ma, Qm Lm and some samples contain peaks at ca. 220 Ma, ca. 75 Ma, and/or ca. 25 Ma.

Provenance Interpretations

All Oligocene–Miocene deposits south of Blue Ridge and the Fenner fault contain substantial ca. 1200 Ma zircon (Fig. 7A), whereas zircon of this age is entirely absent from all such deposits north of Blue Ridge and the Fenner fault (Fig. 7B). This is consistent with a drainage divide along Blue Ridge during the Miocene (Sadler, 1993; Hoyt et al., 2018), and it indicates that this divide was Fk Fp Lv Ls established prior to deposition of the lower Paradise Springs formation, and probably prior to deposition of the Vasquez Formation. Strata north and south Figure 6. Sandstone composition of Oligocene–Miocene strata of Punchbowl block. Composition was of Blue Ridge would thus have formed in distinct basins, hereafter referred to determined using Gazzi-Dickinson point-count method, plotted on QFL, QmFkFp and LmLvLs ternary diagrams, where Q—quartz; F—feldspar; L—nonquartzose lithics; Qm—monocrystalline quartz; Fk— as the “northern” and “southern” subbasins, respectively. potassium feldspar; Fp—plagioclase feldspar; Lm—metamorphic lithics; Lv—volcanic and hypabyssal The granitoid depositionally beneath the Vasquez Formation (compo- lithics; Ls—sedimentary lithics (full definitions of grain categories are in Table 1). Note differences in sitionally near the quadruple point of granite, quartz monzonite, granodio composition and compositional variability among units. Fm.—Formation; fm.—formation. Punchbowl Formation data from Hoyt et al. (2018); all other data of this study; raw data are given in Table S3 (text rite, and quartz monzodiorite on a QAPF diagram [Streckeisen, 1974] and footnote 1). dated as 146 ± 3 Ma 1σ; Table S1 [see footnote 1]) is presumably the primary

A south of Blue Ridge n = 75 Paradise Springs formation

KTC-14-dz4

n = 54 schist breccia of Paradise Springs formation y

KTC-14-dz5

n = 69 Vasquez Formation

KTC-14-dz3

n = 68 Vasquez Formation Figure 7. Relative-probability distributions

r e l a t i v p o b of detrital-zircon U-Pb ages from Oligo- KTC-14-dz2 cene–Miocene strata of Punchbowl block (A) south and (B) north of Blue Ridge. n = 50 Vasquez Formation Within A and B, samples are arranged in approximate stratigraphic order, with youngest on top. Note change of hori- KTC-14-dz1 zontal scale at 300 Ma; vertical scale also differs to left and right of this scale break, north of Blue Ridge such that equal areas represent equal B probability across graph. Labels indicate n = 88 basal Punchbowl Formation sample number and name of geologic unit; n—number of analyses. Sample locations are in Figure 3; raw data are in Table S4 KTC-14-dz8 (text footnote 1). y n = 33 Paradise Springs formation

KTC-14-dz10

n = 69 Paradise Springs formation

KTC-14-dz7

r e l a t i v p o b n = 66 Paradise Springs formation

KTC-14-dz6

0 50 100 150 200 250 300 600900 1200 1500 1800 2100 2400 2700 3000 Age (Ma)

proximal source of the Vasquez Formation. This interpretation accounts for prior to Punchbowl fault slip), where the anorthosite-gabbro-syenite-norite the dominance of granitoid clasts in the conglomerate fraction (Fig. 5), the complex and Mount Lowe intrusion are exposed. This would account for the consistency of sandstone composition with that of both the granitoid and a ca. 1200 Ma and ca. 220 Ma detrital-zircon ages, respectively, in the Vasquez granitoid conglomerate clast (Fig. 6), and the presence of ca. 150 Ma detrital- Formation samples south of Blue Ridge (Fig. 7A), as well as the variability in zircon ages (Fig. 7). South of Blue Ridge, these proximal alluvial-fan deposits sandstone composition (Fig. 6). likely interfingered with more distal deposits shed approximately northward The Paradise Springs formation, in contrast to the Vasquez Formation, from western and central parts of the San Gabriel block (presumably adjacent was derived primarily from the San Francisquito Formation, as documented

by the abundance of sandstone clasts within Paradise Springs conglomerate Structure (Fig. 5), and the greater relative abundance of quartz and sedimentary lithic fragments and lower relative abundance of plagioclase feldspar within Para Blue Ridge Fault dise Springs sandstone (Fig. 6). Because present exposures of San Francis- quito Formation are abundant in the vicinity of Paradise Springs formation South of Blue Ridge, the contact between the Pelona Schist and the Vasquez exposures, but they are absent in most of the area of Vasquez Formation and Paradise Springs formations, mapped as depositional by Dibblee (2002a, exposure (Fig. 3), this contrast in source rock may be more spatial than tem- 2002c), is a fault, here termed the “Blue Ridge fault,” along its entire length. poral. Prominent peaks in the detrital-zircon age distributions at ca. 75 Ma, The fault is poorly exposed, but in places, slickensides and a narrow zone of ca. 150 Ma, and 1660–1800 Ma imply diverse ultimate source rocks. These hydrothermal alteration are present; slickenlines indicate almost pure dip slip are also the dominant zircon ages for the San Francisquito Formation of the (Fig. 3). The Blue Ridge fault terminates to the northwest against the Fenner Soledad region (Jacobson et al., 2011), and so most of this diversity proba- fault. Accordingly, it predates the Fenner and Punchbowl faults, and it is likely bly results from recycling of San Francisquito zircon, rather than direct input a normal fault associated with the phase of extension that much of southern from multiple sources. California underwent beginning ca. 25 Ma (e.g., Tennyson, 1989), in which case North of Blue Ridge, the presence of Pelona Schist clasts in the upper part it would be coeval with deposition of the Vasquez Formation. Truncation of of the Paradise Springs formation, but their absence in the lower part and in Paradise Springs strata indicates that the Blue Ridge fault either remained ac- the underlying Vasquez Formation, represents an unroofing sequence (Fig. 5; tive until this time or was reactivated. Ingersoll and Colasanti, 2004; Colasanti and Ingersoll, 2006). A similar unroofing sequence is present south of Blue Ridge (Fig. 5). The spatially restricted schist breccia within the Paradise Springs formation, interpreted as a proxi- Fenner Fault mal alluvial-fan deposit, is located along the Blue Ridge fault, which bounds the anticlinorium of Pelona Schist along Blue Ridge. This suggests that the North of Blue Ridge, the contact between the Pelona Schist and the San Pelona Schist of Blue Ridge was the source of this breccia, and likely also Francisquito and Vasquez Formations is the Fenner fault. Noble (1954) and the source of the Pelona Schist clasts within the unroofing sequence of the this study (Fig. 3) inferred continuation of the Fenner fault westward through Paradise Springs formation. the Paradise Springs formation to the Punchbowl fault, whereas other studies Basal Punchbowl Formation sandstone is compositionally much more vari- (e.g., Liu, 1990; Weldon et al., 1993; Dibblee, 2002a) have interpreted the Fen- able than that of the overlying Punchbowl Formation, but it is less variable ner fault as predating, and being overlain by, the Paradise Springs formation. than that of the underlying Paradise Springs and Vasquez formations (Fig. 6). Differing interpretations are possible because of poor, discontinuous exposure The basal Punchbowl Formation contains a smaller proportion of gneissic of the Fenner fault in this region. clasts than overlying Punchbowl conglomerate, but a larger proportion than the Paradise Springs and Vasquez formations (Fig. 5). These observations support our interpretation of the basal Punchbowl Formation as documenting the Punchbowl Fault shift in depositional environment from alluvial fans to an integrated braided- fluvial system. In the northern subbasin, a ca. 235 Ma peak is prominent in The Punchbowl fault is a regionally significant strand of the San Andreas the upper Paradise Springs formation (samples KTC-14-dz7 and dz10; Fig. 7B) fault (e.g., Dibblee, 1967), with documented reverse-dextral slip (e.g., Chester and in the basal Punchbowl Formation (sample KTC-14-dz8), but rare or ab- and Chester, 1998). In the southeastern part of the study area, a single fault trace sent down section (sample KTC-14-dz6) and in the San Francisquito Formation is present; to the northwest, the fault splits into two diverging subparallel traces of the Soledad region and the Pelona-Orocopia schist (Jacobson et al., 2011). (Fig. 3; Dibblee, 2002a, 2002c). The northeastern branch dips southwestward, Therefore, the presence of this age peak may document the beginning of this and the dip at the surface is shallower farther northwest (Fig. 3; orientations were change in drainage patterns. The detrital-zircon age distribution for the basal not measured on the southwestern branch). Uplift of the San Gabriel Mountains Punchbowl Formation sample is similar to those of the overlying main mem- has generally been greater in the eastern half, as indicated by higher elevations ber of the Punchbowl Formation (Hoyt et al., 2018), but with more ca. 220 Ma and exposure of deeper structural levels (e.g., Bull, 1987). Accordingly, the pres- zircon and less ca. 245 Ma zircon. This may indicate that the source of the ca. ent surface exposure of the Punchbowl fault within the study area is an oblique 245 Ma zircon, which Hoyt et al. (2018) suggested was likely Middle Triassic view, with progressively deeper structural levels exposed progressively south- plutons of the southern Mojave region (e.g., Barth et al., 1997), was one of the eastward. Splitting of the fault and shallowing of the dip of the northeastern last source areas to become integrated into the developing Punchbowl Forma- branch to the northwest suggest a positive flower structure, in which a nearly tion drainage system. The provenance of the main member of the Punchbowl vertical strike-slip fault at depth splits into two branches, which shallow and ex- Formation was discussed by Hoyt et al. (2018). hibit more reverse slip upward (i.e., Wilcox et al., 1973; Sylvester, 1988).

Smaller Faults and Folds tion to achieve its present, steep northeast dip (Fig. 8B). This rotation was likely also responsible for the steeply southwest-dipping Punchbowl strata in this Faults and folds subparallel to the Punchbowl fault in the Punchbowl For- area (Fig. 3). This fault was likely kinematically linked with the Punchbowl fault mation in the northwestern part of the study area (in the region of A-A′ in and may splay off the Punchbowl fault at depth, as part of the positive flower Figs. 3 and 4) are presumably transpressional features associated with slip and structure proposed above (Figs. 4 and 8). Reverse motion on the Fenner fault shortening along the Punchbowl fault. The fault southeast of the Punchbowl could also be part of this flower structure. syncline (near the middle of A-A′ and B-B′ in Figs. 3 and 4) does not terminate Faults and folds within the San Francisquito Formation and granitoid base- in the basal Punchbowl Formation, as indicated by previous studies (e.g., Dib- ment are subparallel to both the Punchbowl fault and the (presumably older) blee, 2002a), but rather it cuts, and thus postdates, the lower part of the main Blue Ridge fault (Fig. 3), and they could be either high-angle reverse faults and member of the Punchbowl Formation. Additionally, shear-sense indicators associated folds related to transpression, potentially comprising part of the along exposure of this fault zone in a road cut immediately west of B-B′ (Figs. proposed flower structure, or listric normal faults and associated folds related 3 and 4) suggest oblique, reverse-dextral slip. Accordingly, this fault is here to Oligocene–Miocene extension. It is also possible that these faults began interpreted as a transpressional feature related to the Punchbowl fault, rather as normal faults during Oligocene–Miocene extension, and they were subse- than as an extensional feature from earlier in the Miocene. This fault presum- quently reactivated as reverse faults because of their favorable orientation; ably originally dipped southwest (Fig. 8A) and underwent horizontal-axis rota- such reactivation at a larger scale could potentially explain why the trace of the Punchbowl fault so closely follows that of the Blue Ridge fault. These pos- sibilities predict different ages, geometries, and kinematics for these faults; A original geometry B present geometry additional detailed work might clarify these relations. SSW no vertical exaggeration NNE SSW NNE no vertical exaggeration t e Fig. 4: A-A′, Vincent Thrust in cl Fig. 4: D-D′ B-B′, C-C′ yn l s w bo Southwest of the southeastern part of the Punchbowl fault, the Vincent ch n u thrust separates Pelona Schist from mylonitic gneiss (Ehlig, 1981; Jacobson, P f o 1983). Previous mapping (e.g., Dibblee, 2002c) inferred a fault subparallel to th u o s the Punchbowl fault along the southwestern edge of an intrusive body (map (reactivated?) Fenner faul lt u fa unit Pε?gd in Fig. 3) of probable late Oligocene age (May and Walker, 1989;

? ? Nourse, 2002), against which the Vincent thrust terminates. We did not find

? evidence for this fault; rather, our mapping suggests that the Vincent thrust

? was intruded by this intrusive body (Fig. 3). The Vincent thrust may have ? ?

acted as a conduit, along which magma could more easily flow (H-H′ and I-I′ in

Fig. 4); this would explain the anomalously large size of the body intruding the

Punchbowl faul ? Punchbowl faul ? Vincent thrust compared to the surrounding, coeval sills and dikes intruding the Pelona Schist and mylonitic basement (Fig. 3; Dibblee, 2002c).

? ?

t t DISCUSSION

? Basin Development ? Mid-Cenozoic basin development likely began with initiation of normal faulting in the latest Oligocene. Distinct subbasins formed north and south of Blue Ridge, separated by an ancestral Blue Ridge topographic high, which Figure 8. Schematic cross section showing hypothesized positive flower structure along Punchbowl acted as a drainage divide. Relief and erosion along this topographic high were fault: (A) in its initial geometry, and (B) in its present, deformed geometry. This hypothesized structure sufficient to produce the Vasquez Formation alluvial-fan deposits that domi- is composed of two strands of the Punchbowl fault, the Fenner fault (possibly representing reactivation of an older, normal fault), and potentially, the fault south of Punchbowl syncline (Fig. 3). Boxes in B nate the margins of the two subbasins. These proximal deposits interfingered indicate how cross sections of Figure 4 fit this schematic. See text for discussion. with more distal, finer-grained alluvial deposits derived from the opposite

margins of these subbasins. The Pelona Schist along Blue Ridge was entirely nisms, and relationships with surrounding units. The Vasquez Formation of the in the subsurface throughout deposition of the Vasquez Formation, presum- Punchbowl block partly overlaps in sandstone composition with the Vasquez ably covered by the granitoid presently exposed on either side of Blue Ridge Formation of the Soledad region (Fig. 9). In all four regions, lacustrine deposits (Fig. 3), clasts of which dominate the conglomerate fraction of the Vasquez are rare, but where they occur, they are immediately above volcanic strata. The Formation in both subbasins. Extension via normal faulting was accompanied basin geometry we propose for the southern subbasin is analogous to that by bimodal volcanism, which produced the trachyandesite flows and the rhyo described for the Plush Ranch basin of the Tejon region and the Texas Can- lite and trachyandesite conglomerate clasts found in the Vasquez Formation yon subbasin of the Soledad region—a major fault along the southern margin of the southern subbasin (Figs. 3 and 5). The southern subbasin may have that exposed Proterozoic basement and generated large alluvial-fan systems, been primarily a half graben controlled by a normal fault on its southern mar- the fine-grained, distal parts of which interfingered and mixed with proximal, gin, with the Blue Ridge fault forming later as an antithetic normal fault. This coarse-grained deposits shed from granitoid along the northern margin of the would explain both the substantial fine-grained sediment input from the south basin, which was bounded by a smaller, antithetic fault (Hendrix, 1993; Cole implied by detrital-zircon data and tilting of Vasquez strata away from, rather and Stanley, 1995; Hendrix et al., 2010). In both the southern subbasin and the than toward, the Blue Ridge fault (Fig. 3). Texas Canyon subbasin, Vasquez Formation strata and underlying granitoid The northern and southern subbasins persisted until (or were regenerated along the northern margin are in fault contact with an anticlinorium of Pelona during) deposition of the Paradise Springs formation, separated as before by Schist (e.g., Hendrix, 1993). Both the southern subbasin and the Vasquez Rocks an ancestral Blue Ridge drainage divide. Alluvial-fan deposits in these sub subbasin contain interbedded, intermediate volcanic rocks and detritus of the basins were sourced from the San Francisquito Formation and, in the southern anorthosite-gabbro-syenite-norite complex derived from the south (Fig. 10A; subbasin, granitoid and Vasquez volcanic rocks. During deposition of the Para- Hendrix and Ingersoll, 1987). In light of these similarities, the southern sub- dise Springs formation, Pelona Schist was first exposed along Blue Ridge and basin of the central Punchbowl block is likely a close equivalent of the Plush began contributing detritus to both subbasins. Ranch basin of the Tejon region and the Texas Canyon and Vasquez Rocks Following deposition of the Paradise Springs formation, drainage patterns subbasins of the Soledad region. north of Blue Ridge gradually changed, resulting in transition from alluvial-fan to braided-fluvial deposition as the basal member of the Punchbowl Formation Q accumulated. The main member of the Punchbowl Formation accumulated in a well-integrated fluvial system with its headwaters outside the Punchbowl block (Hoyt et al., 2018). A similar transition may have occurred south of Blue Ridge (Hoyt et al., 2018), but no post–Paradise Springs strata are preserved in this part of the Punchbowl block. The southern San Andreas fault became active ca. 5 Ma (Nicholson et al., 1994; Ingersoll and Rumelhart, 1999; Oskin et al., 2001; Crowell, 2003; Oskin and Stock, 2003), with the Punchbowl fault probably representing the initial main trace (Sharp and Silver, 1971). The San Andreas fault has been transpres- F L sional throughout this part of southern California as a result of a restraining Vasquez Formation double bend (term of McClay and Bonora, 2001) of regional scale, extending Qm (Punchbowl block; PεNv): Lm from San Gorgonio Pass (Fig. 1) in the southeast to the Tejon region just north south of Blue Ridge north of Blue Ridge of the Garlock fault in the northwest (e.g., Hill and Dibblee, 1953; Ingersoll and Coffey, 2017). This transpression shut down the Punchbowl drainage system Vasquez Formation and caused uplift, deformation, and erosion of Oligocene–Miocene strata. (Soledad region) south of Sierra Pelona north of Sierra Pelona

Regional Stratigraphic Correlations

Vasquez Formation Fk Fp Lv Ls

The Vasquez Formation of the Punchbowl block generally resembles the Figure 9. Comparison of sandstone composition of Vasquez Formation of Punchbowl block and Vasquez Formation of Soledad region, which are likely correlative. Details are as in Figure 6. Plush Ranch, Vasquez, and Diligencia Formations of the Tejon, Soledad, and Soledad region data are from Hendrix (1986); Punchbowl block data are from this study (Table S3 Orocopia regions, respectively, in terms of age, lithology, depositional mecha- [text footnote 1]).

GEOSPHERE | Volume 15 | Number 2 Coffey et al. | Stratigraphy, provenance, and tectonic significance of the Punchbowl block Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/2/479/4663930/479.pdf 491 by guest on 01 October 2021 on 01 October 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/2/479/4663930/479.pdf Research Paper Plush Ranch basin and Arthur (1982). and Arthur (2005a, 2005b); Soledad region: Sams (1964), Hendrix and Ingersoll (1987), Dibblee (1997), Coffey (2015); Punchbowl block: Dibblee (1987), this study; Orocopia region: Spittler block: this study. (B) Basins north of Blue Ridge, Sierra Pelona, and equivalent bodies of Pelona-Orocopia schist. Sections are based on following sources: Tejon region: Dibblee schist. Sections are based on following sources: Tejon region: Carman (1964), Dibblee (2006a); Soledad region: Hendrix and Ingersoll (1987), Dibblee (1996a, 2996b); Punchbowl at base of Oligocene–Miocene strata. Units of matching color are likely correlative. (A) Basins south of Blue Ridge, Sierra Pelona, and equivalent bodies of Pelona-Orocopia west (left) to east (right). Approximate present locations of these sections are shown in Figure 1. Tick marks along left margins of columns are spaced every 1000 m and begin Figure 10. Schematic composite stratigraphic sections for Oligocene–Miocene strata of Punchbowl block, and Tejon, Soledad, and Orocopia regions. Sections are arranged from TEJON REGION : TEJON REGION : A B Simmler basi

basins south of schist exposure basins north of schist exposure

. Fm Pattiway unnamed marine unnamed unconformity angular angular unconformity Formation Va Simmle Caliente Fm. Quatal Fm . Caliente Fm. Quatal Fm . disconformity? angular unconformity n angular unconformity queros Fm . Formation Plush Ranch

a strat Charlie Canyon subbasin T exas Canyon subbasin SOLEDAD REGION: SOLEDAD REGION: Ti angular unconformity partly conformabl Formation San Francisquit V Mint Canyon Fm. Castaic Fm . angular unconformity Formation Pelona fault

Saugus Fm Formation Va angular unconformity Formation Mint Canyon angular unconformity Saugus Fm .

Tick Canyon strata asque ck Canyon strata unconformity? sque z s s z

. e o V PUNCHBOWL asquez Rocks subbasi SOLEDAD REGION: northern subbasin (rock-avalanche breccia) upper Oligocene - lower Miocene middle Miocene middle Miocene - lower Pliocen Pliocene - Quaternary nonconformities BLOCK: San Francisquito Fm Formation Punchbow Quaternary alluvium Formation Va Ti Formation Mint Canyon nonconformity conformable partl y V Castaic Fm . angular unconformity angular unconformity asquez Fm . angular unconformity Paradise Springs fm ck Canyon strata sque z unconformity? n l

e . PUNCHBOW OROCOPIA . AGE: southern subbasin crystalline basemen strata, and interbedded alluvial deposits volcanic flows, associated lacustrine and conglomerate marine shale and minor sandstone conglomerate and shal marine sandstone and minor rock-avalanche brecci fine sandstone, limestone and evaporites lacustrine mudstone, siltstone fluvial siltstone and sandstone fluvial conglomerate and sandston alluvial sandstone and fine conglomerate alluvial conglomerate and sandstone Diligencia basin pre-Cenozoic upper Cretaceous - Eocene (general) upper Oligocene - lower Miocene (volcanic flows & associated strata upper Oligocene - lower Miocene nonconformity nonconformities REGION : LITHOLOG Y: Blue Ridge fault L BLOCK: unconformity Maniobra Fm angular unconformity Formatio n Diligencia Quaternary alluvium Formatio n Va Paradise Springs fm Punchbowl fault angular unconformity sque z t a e ? , . e . )

GEOSPHERE | Volume 15 | Number 2 Coffey et al. | Stratigraphy, provenance, and tectonic significance of the Punchbowl block 492 Research Paper

The northern subbasin of the Punchbowl block lies north of the Fenner (Sams, 1964; Ehlert, 1982, 2003; Hendrix, 1993; Weber, 1994; Dibblee, 1997; fault and Blue Ridge anticlinorium, a position analogous to that of the Charlie Coffey, 2015). Additionally, both units overlie sandstone, conglomerate, Canyon subbasin of the Soledad region (e.g., Dibblee, 1997), with which it is and coeval volcanic strata of the Vasquez Formation, and both are overlain likely equivalent. Similar rockslide megabreccias near the top of the Vasquez by Middle–Upper Miocene sandstone and conglomerate with no signifi- Formation in each subbasin (Fig. 10B; Sams, 1964; Weber, 1994; Dibblee, 1997) cant angular discordance (Fig. 10). The Paradise Springs formation of the support this correlation. These subbasins may also correlate with the Simmler southern subbasin presumably correlates with the type Tick Canyon strata, Formation north of Pelona Schist exposures in the Tejon region. Consistent south of Sierra Pelona, whereas that of the northern subbasin presumably with this correlation, there is a general increase in clast size up section in both correlates with the Tick Canyon strata of Charlie Canyon subbasin, north of the Charlie Canyon subbasin (Sams, 1964; Hendrix and Ingersoll, 1987) and Sierra Pelona. the Simmler Formation (Fig. 10B; Dibblee, 2005a, 2005b). The Diligencia For- mation occupies an analogous position north of the Orocopia Mountains anticlinorium in the Orocopia region, and thus may correlate with these basins as Punchbowl Formation well (Fig. 10B; Ingersoll et al., 2014). The Punchbowl Formation is largely coeval with the Caliente and Mint Canyon Formations of the Tejon and Soledad regions, respectively, but it Paradise Springs Formation represents a distinct drainage system (Hoyt et al., 2018). Strata mapped as Punchbowl Formation are present southeast of Sierra Pelona, at the The Paradise Springs formation resembles the Tick Canyon strata of the eastern edge of the Soledad region (e.g., Dibblee, 2001). A sample of these Soledad region: Both represent primarily alluvial-fan deposits with highly strata analyzed by Coffey (2015) closely matched those of the Punchbowl variable and partly overlapping sandstone composition (Fig. 11), and both Formation of the Punchbowl block (Hoyt et al., 2018) in both sandstone contain unroofing sequences documenting exhumation of Pelona Schist composition and detrital-zircon age distributions, suggesting that these strata are indeed part of the Punchbowl Formation. Additional sampling and study of these strata would be required to determine their paleogeo- Q graphic significance.

Regional Tectonic and Paleogeographic Reconstructions

Punchbowl Fault

Previous correlation of the central Punchbowl block and the Soledad region has been based on correlation of (1) the anticlinoria of Pelona Schist along F L Blue Ridge and Sierra Pelona, (2) the Fenner and San Francisquito faults along Paradise Springs formation the northern margins of these anticlinoria, and (3) the presence of San Fran- Qm (Punchbowl block; Nps) Lm cisquito Formation north of these anticlinoria (Dibblee, 1967, 1968; Ehlig, 1968, south of Blue Ridge north of Blue Ridge 1981; Powell, 1993). Our correlation of Oligocene–Miocene strata on either side of these anticlinoria confirms these correlations, and the 40–50 km of dextral Tick Canyon strata slip on the Punchbowl fault that they imply. (Soledad region) south of Sierra Pelona

San Gabriel/Canton and San Andreas Faults

Our findings support reconstructions of the San Gabriel/Canton and San Fk Fp Lv Ls Andreas faults that closely align crustal blocks of the Tejon, Soledad, and Orocopia regions (e.g., Hill and Dibblee, 1953; Crowell, 1962, 1975a; Carman, Figure 11. Comparison of sandstone composition of Paradise Springs formation of Punchbowl block and Tick Canyon strata of Soledad region, which are likely correlative. Details are as in 1964; Ehlig and Ehlert, 1972; Bohannon, 1975; Ehlert, 1982, 2003; Weigand, Figure 6. All data are from this study (Table S3 [text footnote 1]). 1982; Frizzell and Weigand, 1993; Ingersoll et al., 2014; Hoyt et al., 2018).

In particular, the presence of Oligocene–Miocene strata on both flanks of the mations, which are truncated by the San Francisquito–Fenner–Clemens Well Blue Ridge anticlinorium helps link the Soledad region, where strata south fault (e.g., Jahns and Muehlberger, 1954; Muehlberger, 1958; Crowell, 1975b). of the Sierra Pelona anticlinorium have been given greater emphasis (e.g., Whereas the San Francisquito–Fenner–Clemens Well fault is largely high Crowell, 1975a; Hendrix and Ingersoll, 1987), with the Orocopia region, where angle and bears evidence of some dextral slip (e.g., Crowell, 1962; Stanley, Oligocene–Miocene strata are presently preserved only on the north side of 1966; Konigsberg, 1967; Spittler and Arthur, 1982; Terres, 1984; Ebert, 2004; its anticlinorium (e.g., Crowell, 1975b). Correlating the Diligencia basin of the Yan et al., 2005), it has been suggested that this represents minor (i.e., ≤10 km; Orocopia region with the Charlie Canyon subbasin of the Soledad region (e.g., Crowell, 1962; Spittler and Arthur, 1982; Terres, 1984; Ebert, 2004) reactivation Bohannon, 1975; Ingersoll et al., 2014), using the northern subbasin of the cen- of what was originally an Oligocene–Miocene normal fault (e.g., Spittler and tral Punchbowl block as the link, eliminates problems with correlation of the Arthur, 1982; Hendrix and Ingersoll, 1987; Goodmacher et al., 1989; Robinson Soledad and Orocopia regions (e.g., those discussed by Law et al., 2001). and Frost, 1996; Bunker and Bishop, 2001; Yan et al., 2005; Jacobson et al., 2007; Ingersoll et al., 2014). We suggest that down-to-north normal faulting along the Fenner fault likely contributed to subsidence of the northern sub San Francisquito–Fenner–Clemens Well Fault basin of the central Punchbowl block.

The similarity of the stratigraphic sequences in the northern and southern subbasins of the central Punchbowl block argues against the proposed Synthesis 80–110 km of dextral slip along the Fenner fault (and the correlated San Fran- cisquito and Clemens Well faults; Powell, 1981, 1993), which separates the two Correlation of Oligocene–Miocene strata of the central Punchbowl block subbasins. In particular, the presence of clasts of San Francisquito Formation with those of the Tejon, Soledad, and Orocopia regions supports the hypothe- sandstone in Paradise Springs formation conglomerate of the southern sub- sis that all four crustal blocks were aligned prior to slip along the San Gabriel/ basin (Fig. 5) seems incompatible with this magnitude of slip. These clasts Canton and San Andreas/Punchbowl faults (e.g., Hill and Dibblee, 1953; link the southern subbasin, which is south of the Fenner fault, with the San Crowell, 1962, 1975a; Carman, 1964; Dibblee, 1967, 1968; Ehlig, 1968, 1981; Ehlig Francisquito Formation, which is north of the Fenner fault (Fig. 3). Even if and Ehlert, 1972; Bohannon, 1975; Ehlert, 1982, 2003; Weigand, 1982; Frizzell deposition of the Paradise Springs formation occurred after this proposed Fen- and Weigand, 1993; Ingersoll et al., 2014; Hoyt et al., 2018). Combining these ner fault slip, the presence of a drainage divide along Blue Ridge throughout correlations with paleomagnetic data (Terres, 1984; Terres and Luyendyk, 1985; deposition of the Paradise Springs formation, discussed above, would have Hornafius et al., 1986; Carter et al., 1987; Ellis et al., 1993), and stratigraphic prevented transport of these clasts across the Fenner fault into the southern and provenance data (see references above and in Fig. 12 caption), we pro- subbasin. Rather, these clasts are presumably derived from San Francisquito pose the following sequence of paleogeographic reconstructions: (1) Normal Formation outcrops originally present south of the Fenner fault. Furthermore, faulting initiated ca. 25 Ma, forming two parallel belts of basins separated by whereas restoration of 60–70 km of dextral slip on the San Gabriel/Canton fault a topographic high along Sierra Pelona (Hendrix and Ingersoll, 1987) and Blue aligns the Simmler Formation of the Tejon region with its likely correlative, the Ridge. Alluvial-fan deposits, partly sourced from this topographic high, and Vasquez Formation of the Charlie Canyon subbasin of the Soledad region (e.g., bimodal volcanic flows accumulated in these basins (Fig. 12A). (2) The Canton Ingersoll et al., 2014), restoration of 80–110 km of dextral slip along the San fault (precursor to the San Gabriel fault; e.g., Crowell, 2003) initiated ca. 18 Ma. Francisquito–Fenner–Clemens Well fault, as proposed by Powell (1981, 1993), East of the Canton fault, Pelona-Orocopia schist was exhumed along the an- would eliminate this cross-fault match. cestral Sierra Pelona/Blue Ridge/Orocopia Mountains topographic high (e.g., If dextral slip of 80–110 km accumulated along the San Francisquito– Sams, 1964; Konigsberg, 1967) as these crustal blocks underwent clockwise Fenner–Clemens Well fault, then most or all of it would have done so in the few vertical-axis rotation (Fig. 12B). Exposed Pelona Schist contributed detritus to million years after deposition of the Vasquez and Diligencia Formations, and alluvial-fan deposits on either side of this topographic high. (3) Beginning ca. before deposition of the Paradise Springs formation and Tick Canyon strata 15 Ma, braided-fluvial systems began to develop on either side of the ancestral (Fig. 2). Unroofing sequences document exhumation of the Pelona Schist in Sierra Pelona/Blue Ridge/Orocopia Mountains topographic high. By ca. 13 Ma, the northern subbasin of the Punchbowl block (Paradise Springs formation; these fluvial systems were established, with the intervening topographic high Ingersoll and Colasanti, 2004; Colasanti and Ingersoll, 2006; this study) and in continuing to act as a drainage divide (Fig. 12C). (4) Continued dextral slip the Charlie Canyon subbasin of the Soledad region (Tick Canyon strata; Sams, along the Canton fault and its successor, the San Gabriel fault (e.g., Crowell, 1964; Weber, 1994; Dibblee, 1997; Coffey, 2015). These unroofing sequences 2003), displaced the Tejon block from its eastern equivalents. This disrupted link these strata, which are north of the San Francisquito–Fenner–Clemens the Caliente/Mint Canyon drainage system and allowed a marine incursion Well fault, with the Pelona Schist anticlinoria south of this fault. Any significant into the western Soledad region, where the Castaic Formation began to ac- dextral slip must have postdated deposition of the Vasquez and Diligencia For- cumulate (Fig. 12D; e.g., Crowell, 1954; Ehlert, 1982). The Punchbowl drainage

GEOSPHERE | Volume 15 | Number 2 Coffey et al. | Stratigraphy, provenance, and tectonic significance of the Punchbowl block Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/2/479/4663930/479.pdf 494 by guest on 01 October 2021 on 01 October 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/2/479/4663930/479.pdf Research Paper Springs formation, north of and south of, respectively, Blue Ridge; TCC —Tick Canyon strata, Charlie Canyon; TCT —Tick Canyon strata, type locality. (precursor to San Gabriel fault) is active, and crustal blocks on its eastern side are undergoing vertical-axis clockwise rotation. PSN , Pelona/Blue Ridge drainage divide and contributes detritus to alluvial-fan deposits accumulating on either side of this divide. Dextral Canton fault during deposition of Paradise Springs formation18 Ma, and Tick Canyon strata. Pelona-Orocopia schist has been exhumed along ancestral Sierra Vasquez Formation of Punchbowl block, southern and northern subbasins, respectively; VR —Vasquez Formation, Vasquez Rocks subbasin. (B) Ca. subbasin; (or Big Pine) fault; Pf—Pelona fault; Sf—Soledad fault; VCf—Vasquez Canyon fault. Sedimentary deposits: CC —Vasquez Formation, Charlie Canyon CWf—Clemens Well fault; Df—Diligencia fault; Ff—Fenner fault; OMf—Orocopia Mountains fault; SFf—San Francisquito fault; LVf—Lockwood Valley raphy: ABR—ancestral Blue Ridge; ASP—ancestral Sierra Pelona; MCR—Mint Canyon Ridge; Mt.—Mount. Active faults (red): BRf—Blue Ridge fault; Pelona/Blue Ridge drainage divide separates two parallel belts of basins, in which alluvial-fan deposits and volcanic flows accumulate. Paleogeog Ma, during deposition of Vasquez,Soledad-Punchbowl-Orocopia regions. (A) Ca. Plush Ranch, 23 and Diligencia Formations. An ancestral Sierra Figure 12 ( on this and following page). Schematic representation of interpreted paleogeography, source rocks, and depositional systems of Tejon- B A ca. 23 Ma - Va ca. 18 Ma - Paradise Springs formation

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GEOSPHERE | Volume 15 | Number 2 Coffey et al. | Stratigraphy, provenance, and tectonic significance of the Punchbowl block 495 on 01 October 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/2/479/4663930/479.pdf Research Paper Ingersoll and Coffey (2017), Hoyt et al. (2018), and other ideas references presented in text. with sediment by Punchbowl drainage system. Details of A–D are after Crowell (1975a), Hendrix and Ingersoll (1987), Link (2003), Ingersoll et al. (2014), and its successor, San Gabriel fault, has displaced Tejon block northwest. Marine deposition has begun in western Soledad region, possibly supplied 9 Ma, during deposition of younger parts of Punchbowl and Caliente Formations, and of Castaic Formation. Continued dextral slip along Canton fault complete (though subsequent rotations that bring these blocks into their modern orientations have yet to occur). P —Punchbowl Formation. (D) Ca. has given way to braided-fluvial deposition. Dextral slip continues to accumulate along Canton fault. Clockwise rotation already under way in B is now Figure 12 ( continued TEJON REGION C Formatio n Punchbowl Formation (upper D Calient M o d e l ca. 13 Ma - Punchbowl Formation (lower

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GEOSPHERE | Volume 15 | Number 2 Coffey et al. | Stratigraphy, provenance, and tectonic significance of the Punchbowl block 496 Research Paper

system may have supplied sediment to the Castaic Formation and/or breached Alabama) of the University of California, Los Angeles (UCLA) for help with sample preparation. We the ancestral Sierra Pelona/Blue Ridge drainage divide to deliver sediment to thank An Yin for helpful comments on the M.S. thesis upon which this paper is largely based, and Carl Jacobson for useful discussion. We thank Peter Haproff, Randon Flores, and Drew Gomberg the eastern Soledad region. The northern Caliente Formation, which is com- for discussion of map relationships, and the camp at Paradise Springs for access to its property. We positionally distinct from the rest of the Caliente Formation (Hoyt et al., 2018), also thank Bryan Murray and Kim Bishop for helpful review of a previous version of this manuscript. may have formed during this time as well. (5) Slip began along the south- Fieldwork and microscope thin sections were paid by a Graduate Student Research Grant from the Geological Society of America awarded to Kevin T. Coffey. Detrital-zircon analyses were paid ern San Andreas fault ca. 5 Ma, inducing transpression, which shut down the by a UCLA Academic Senate research grant awarded to Raymond V. Ingersoll. The ion-micro- Punchbowl drainage system and deformed and uplifted Oligocene–Miocene probe facility at UCLA is partly supported by a grant from the Instrumentation and Facilities Pro- strata. Slip along the Punchbowl fault, probably the initial trace of the southern gram, Division of Earth Sciences, National Science Foundation. The Arizona LaserChron Center is partly supported by National Science Foundation grant EAR-1032156. San Andreas fault, separated the Soledad block from the Punchbowl block. Following abandonment of the Punchbowl fault in favor of the present trace of the southern San Andreas fault, the Punchbowl block was separated from the Orocopia block. Shortening between the southern Sierra Nevada and northern REFERENCES CITED Peninsular Range batholiths likely induced additional vertical-axis rotations Advocate, D.M., Link, M.H., and Squires, R.L., 1988, Anatomy and history of an Eocene sub along the San Andreas fault system, bringing the crustal blocks in Figure 12D marine canyon: The Maniobra Formation, southern California, in Filewicz, M.V., and Squires, into their present orientations (e.g., Ingersoll and Coffey, 2017). R.L., eds., Paleogene Stratigraphy, West Coast of North America [Book 58]: Pacific Section, Society of Economic Paleontologists and Mineralogists (SEPM), Los Angeles, p. 45–58. Alroy, J., 2000, New methods for quantifying macroevolutionary patterns and processes: Paleo biology, v. 26, p. 707–733, https://doi.org/10.1666/0094-8373(2000)026<0707:NMFQMP>2.0 CONCLUSIONS .CO;2. Anderson, J.L., and Bender, E.E., 1989, Nature and origin of Proterozoic A-type granitic magmatism in the southwestern United States of America: Lithos, v. 23, p. 19–52, https://doi.org/10 Oligocene–Miocene strata of the central Punchbowl block are composed .1016/0024-4937(89)90021-2. of three distinct units: the Vasquez, Paradise Springs, and Punchbowl forma- Barth, A.P., and Wooden, J.L., 2006, Timing of magmatism following initial convergence at a tions. These strata were deposited in distinct subbasins north and south of a passive margin, southwestern U.S. Cordillera, and ages of lower crustal magma sources: The Journal of Geology, v. 114, p. 231–245, https://doi.org/10.1086/499573. drainage divide along what is now Blue Ridge. 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