Army Corps of Engineers USACE endpoint is here
https://services7.arcgis.com/n1YM8pTrFmm7L4hs/ArcGIS/rest/services
How to explore this REST api endpoint?
https://transparentgov.net/json2tree/esri/server/folder.html?org=&url=&select_folder=1&select_layer=5
https://transparentgov.net/json2tree/esri/server/folder.html?org=https%3A%2F%2Fservices7.arcgis.com%2Fn1YM8pTrFmm7L4hs%2FArcGIS%2Frest%2Fservices&url=https%3A%2F%2Fservices7.arcgis.com%2Fn1YM8pTrFmm7L4hs%2FArcGIS%2Frest%2Fservices&select_folder=1&select_layer=
https://transparentgov.net:3200/googlemaps/default?layer_id=0&layer=Recreation+Area¢er_lat=38.03144509965616¢er_long=-80.13717068559815¢er_zoom=5&url=https%3A%2F%2Fservices7.arcgis.com%2Fn1YM8pTrFmm7L4hs%2FArcGIS%2Frest%2Fservices%2Fusace_recreation_areas%2FFeatureServer&overlayType=overlayType_none&panto=0
More example
Copy and paste following sample URL ( or your arcgis rest api endpoint URL ) next to 'let's go' button, then click 'enter' key or 'let's go' button
1). Arcgis Online ( Palm Springs, CA ):
https://services.arcgis.com/f48yV21HSEYeCYMI/arcgis/rest/services
2). Arcgis Portal ( HRSA ):
https://gisportal.hrsa.gov/server/rest/services
3). Arcgis Server ( USGS ):
https://gis.usgs.gov/padus/rest/services
4). Arcgis Server ( La Quinta, CA ):
https://gis.la-quinta.org/arcgis/rest/services