Cooperative National Geologic Map: Earth’s surface geology

The USGS National Cooperative Geologic Mapping Program (NCGMP) was directed by Congress to create a new geologic map of the United States” by “bring[ing] together detailed national and continental-resolution 2D and 3D information produced throughout the Survey and by federal and state partners” (House Report 116-100). To fulfill this goal, the NCGMP created a map synthesis engine (Johnstone and others, 2025) based on the Geologic Map Schema (GeMS) standard (NCGMP, 2020) and used it to bring together source geologic maps originally published by the USGS and State Geological Surveys. This thematic map layer was derived from this database using procedures described by Johnstone and others (2025) and is intended to serve as a legible national map of the nation; while it retains full descriptions of geologic units from source materials it does not include the full search functionality (described in Johnstone and others, 2025) that is facilitated by a true relational database.
The Earth’s Surface Geology layer depicts geologic units exposed at the earth’s surface over the entire conterminous United States, inclusive of everything from Quaternary glacial deposits to Precambrian crystalline bedrock. In the West and Southeast, the map is a composite of 29 state geologic maps depicting geology at the earth’s surface. In the glaciated region of the Midwest and Northeast, the map is a composite of 21 state geologic maps depicting pre-Quaternary rocks (“bedrock”), 8 state geologic maps depicting Quaternary deposits, and 18 USGS Quaternary Atlas Series maps depicting Quaternary deposits; the Quaternary Atlas maps were used where modern state geologic maps were not available. Quaternary and pre-Quaternary maps were composited by replacing bedrock, residuum, and colluvium (as identified in the GeMS Geomaterials field) on Quaternary maps with the corresponding content from the underlying pre-Quaternary maps (including line and point features). The map is structured as a single GeMS database with three additional tables (also described in Johnstone and others, 2025); a Source_DescriptionOfMapunits table preserves all source inputs, a synthesis_to_source_units table relates aggregated national units to original map units, and a Symbol_Lookup table provides definitions of all FGDC geologic map symbol code values (U.S. Geological Survey, 2006) used for stylizing the map.

美国地质调查局（USGS）国家合作地质填图计划（NCGMP）受国会委托，需整合美国地质调查局及联邦、州级合作伙伴产出的全套国家级与大陆尺度二维、三维精细数据，以此编制美国全新地质图件（众议院报告第116-100号）。为达成该目标，NCGMP基于地质图模式（Geologic Map Schema, GeMS）标准（NCGMP, 2020）开发了地图合成引擎（Johnstone等，2025），并依托该引擎整合了由USGS与州地质调查局原始发布的源地质图件。本专题地图图层即基于该数据库，遵循Johnstone等（2025）所述流程生成，旨在产出一份清晰可读的美国国家级地质图件；其虽完整保留了源材料中地质单元的描述信息，但未具备真实关系数据库所支持的完整检索功能（详见Johnstone等，2025）。
地表地质图层展示了美国本土全境出露于地表的地质单元，涵盖从第四纪冰川沉积到前寒武纪结晶基岩的全部类型。在美国西部与东南部地区，本地图为29份表征地表地质情况的州地质图件的合成产物。在中西部与东北部冰川作用区域，本地图由三类图件合成而来：21份表征前第四纪岩石（即“基岩”）的州地质图件、8份表征第四纪沉积的州地质图件，以及18份USGS第四纪图集系列地图（用于填补无现代州地质图件覆盖的区域）。第四纪与前第四纪图件的合成规则为：将第四纪图件中GeMS地质材料字段所标识的基岩、残积层与坡积层，替换为下伏前第四纪图件对应的内容（含线与点要素）。本地图采用单一GeMS数据库结构，并额外增设3张数据表（详见Johnstone等，2025）：其中Source_DescriptionOfMapunits表留存所有源输入信息，synthesis_to_source_units表用于关联聚合后的国家级单元与原始图件单元，Symbol_Lookup表则提供了用于地图整饰的全部联邦地理数据委员会（Federal Geographic Data Committee, FGDC）地质图符号编码值（美国地质调查局，2006）的定义。