Opinion for the Court filed by Circuit Judge SENTELLE.
SENTELLE, Circuit Judge:
This is an appeal by the Secretary of the Interior and intervenor National Mining Association ("NMA") from a judgment of the District Court. The District Court held that the Secretary's interpretation of the Surface Mining Control and Reclamation Act's ("SMCRA") section 701(28), 30 U.S.C. § 1291(28) (2000), to exclude subsidence from the definition of "surface coal mining operations" regulated under section 522(e) of the Act, 30 U.S.C. § 1272(e), was contrary to the law and therefore invalid. Because we find that Congress did not speak unambiguously on this precise issue in the SMCRA and because we find the Secretary's interpretation to be reasonable, we defer to the Secretary and reverse the District Court.
A. The Litigation
This case began with Citizens Coal Council's ("CCC") challenge to the Secretary of the Interior's final rulemaking action by which she promulgated the regulation contained in 30 C.F.R. § 761.200 (2003). The challenged regulation is an interpretive rule, based on sections 701(28) and 522(e) of the SMCRA, 30 U.S.C. § 1201, et seq. The regulation states:
30 C.F.R. § 761.200. CCC sought review of this rulemaking in District Court, after exhausting its administrative remedies. It claimed that the Secretary's interpretation of the cited provisions of the SMCRA was contrary to the clear law, and therefore, unworthy of any deference by the courts. As a remedy, CCC requested that the court vacate the regulation and instruct the Secretary to impose instead, a regulation stating that subsidence was included within 701(28)'s definition. The District Court granted CCC's motion for summary judgment holding that "Congress has expressed its intent clearly on the precise point at issue here and that the Secretary's interpretation of § [701(28)] and § [522(e)] is contrary to law." Citizens Coal Council v. Norton, 193 F.Supp.2d 159, 165 (D.D.C.2002). The District Court then remanded the regulation to the Secretary without instruction.
CCC filed a notice of appeal on April 11, 2002, and intervenor NMA filed its notice the following day. On June 5, 2002, the District Court granted the appellant's motion to stay the remand order, but vacated the regulation and stayed its judgment pending appeal. See Citizens Coal Council v. Babbitt, No. 00-0274 (June 5, 2002). On June 6, 2002, the Secretary filed a notice of appeal of both rulings. In the present case, the Secretary and NMA appeal the District Court's ruling that the regulation was invalid and its subsequent vacation of the regulation, and CCC appeals the District Court's refusal to grant the full relief it requested.
B. The Statutory Scheme
We recognize from the outset that the SMCRA is a complex and often puzzling statute, in many cases raising a variety of questions as to its correct interpretation. SMCRA was enacted in an effort by Congress to both "protect society and the environment from the adverse effects of surface coal mining operations" and to "assure that the coal supply essential to the Nation's energy requirements, and to its economic and social well-being is provided and strike a balance between protection of the environment and agricultural activity and the Nation's need for coal as an essential source of energy." 30 U.S.C. § 1202(a), (f). As the District Court recognized and the parties do not dispute, the focus of the regulation in SMCRA was primarily on the surface mining techniques, such as strip-mining, and one of its goals was to encourage the development and application of underground mining technologies as an alternative less likely to disturb lands used for other activities. See Citizens Coal, 193 F.Supp.2d at 161 (citing 30 U.S.C. §§ 1201, 1202(k)).
To this purpose, SMCRA section 522(e) prohibits "surface coal mining operations" with certain exceptions, in a number of protected areas, particularly within the boundaries of the national parks system, national forests, and public parks and historic sites. In addition, these operations are also prohibited "within  feet of the outside right-of-way line of any public road"; "within  feet from any occupied dwelling, unless waived by the owner thereof"; and "within  feet of any public building, school, church, community, or institutional building, public park, or within  feet of a cemetery." 30 U.S.C. § 1272(e)(4), (5).
SMCRA section 701(28) defines "surface coal mining operations" as follows:
30 U.S.C. § 1291(28). SMCRA section 516(a) requires the Secretary to promulgate rules and regulations directed toward "the surface effects of underground coal mining operations" embodying the requirements of section 516(b), but instructs the
30 U.S.C. § 1266(b)(1). Section 516(c) extends the Secretary's authority to regulate underground coal mining if it creates a danger to inhabitants.
30 U.S.C. § 1266(c). Section 516(d) extends the subchapter to cover "surface operations and surface impacts incident to underground coal mining operations."
30 U.S.C. § 1266(d).
We review the Secretary's interpretation of the provisions of the SMCRA, a statute she administers, under the analysis articulated in Chevron, U.S.A. Inc. v. Natural Res. Def. Council, Inc., 467 U.S. 837, 104 S.Ct. 2778, 81 L.Ed.2d 694 (1984). The two-step test of Chevron requires, first, that both the agency and the courts give effect to Congress's unambiguously expressed intent if the underlying statute speaks directly to the precise question at issue. Chevron, 467 U.S. at 842-43, 104 S.Ct. at 2781-82. In this first analytical step, the courts use "traditional tools of statutory interpretation-text, structure, purpose, and legislative history." Pharm. Research & Mfrs. of Am. v. Thompson, 251 F.3d 219, 224 (D.C.Cir.2001). If, however, the statute is "silent or ambiguous with respect to the specific issue" the court must defer to the agency's interpretation if it is reasonable. Chevron, 467 U.S. at 843, 104 S.Ct. at 2782. Because we find that the term "surface impacts incident to an underground coal mine" as it appears in section 701(28) does not unambiguously include subsidence, the second step of Chevron requires that we defer to the Secretary's reasonable interpretation of the statute and reverse the District
We begin, as always, with the plain language of the statute in question. The Secretary interprets the definition of "surface coal mining operations" contained in 701(28), and thereby prohibited in 522(e), to exclude subsidence. The Secretary first argues that the plain meaning of the word "operations" suggests a reference to some human activity, and not to a possible effect of underground mining, like subsidence. See Webster's Third New International Dictionary 1581 (1971) (defining "operation" as "doing or performing"). If 701(28)'s definition ended after its first phrase, "activities conducted on the surface of lands in connection with a surface coal mine or subject to the requirements of section 516 surface operations," this interpretation might be more clearly compelled. However, as CCC points out, the phrase which follows: "surface operations and surface impacts incident to an underground coal mine" could add significantly to the scope of the term "operations" as used in this context.
As the District Court noted, the Secretary essentially parses the definition to read "activities conducted on the surface of lands in connection with  a surface coal mine or  subject to the requirements of section 1266 of this title[,] surface operations and surface impacts incident to an underground coal mine...". Citizens Coal, 193 F.Supp.2d at 163 (citing 30 U.S.C. § 1291(28)(A)). The Secretary supports this interpretation with the definition's next sentence which begins with the phrase "[s]uch activities." This phrase is repeated throughout the remainder of the definition, and is defined within the provision by the examples of activities listed, e.g., excavation; physical or chemical processing; and loading for interstate transport. See 30 U.S.C. § 1291(28)(A). The Secretary therefore concludes that the opening sentence refers to these "activities" only. The District Court held that this reading was not "the most natural" one, in light of the legislative history and the overall purpose of the Act. See Citizens Coal, 193 F.Supp.2d at 163-64. The reading advanced as the "most natural" by CCC and accepted by the District Court "becomes apparent with the addition of three commas" as follows: "`surface coal mining operations' means — (A) activities conducted on the surface of lands in connection with a surface coal mine[,] or [,] subject to the requirements of section 1266 of this title [,] surface operations and surface impacts incident to an underground coal mine...." Id. at 163. The District Court and CCC therefore read 701(28) to mean the surface coal mining operations — prohibited in areas specified by 522(e) — to include as a separate matter "surface impacts" incident to an underground mine, which must then include subsidence.
We need not disavow the District Court's determination that CCC's tendered interpretation is the more natural one in order to reverse the District Court and uphold the Secretary. As noted by the District Court we have, on a previous occasion, observed that "[t]he most natural reading of the [SMCRA] as a whole, and the definition in [§ 1291(28)] in particular ... then suggests that `surface coal mining operations' encompasses both surface coal mines and the surface effects of underground mines." Citizens Coal, 193 F.Supp.2d at 163 (quoting Nat'l Wildlife Fed'n v. Hodel, 839 F.2d 694, 753 (D.C.Cir.1988)). Even assuming the correctness of our reasoning and that of the District Court, the ambiguity of the statute in combination with the Chevron doctrine eclipses the ability of the courts to substitute their preferred interpretation for an agency's reasonable interpretation when that agency is the entity authorized to administer the statute in question. See, e.g., NMA v.
Both parties argue that the legislative history of the SMCRA supports its interpretation. CCC relies on several statements in the Senate and House reports relating to SMCRA's promulgation. According to CCC, the Senate report indicates that SMCRA was addressed to "surface coal mining operations-including exploration activities and the surface effects of underground mining." S.REP. No. 95-128, at 49 (1977). CCC contends that the report clarifies that those effects include subsidence, quoting a discussion in the report on the environmental hazards posed by coal mining: "Similar hazards also occur from the surface effects of underground coal mining, including the dumping of coal waste piles, subsidence and mine fires." Id. at 50. Additionally, the report states that the Act's initial regulatory requirements extended to "[a]ll surface coal mining operations, which include, by definition surface impacts incident to underground coal mines." Id. at 71. The District Court relied on this passage from the report to support its position that section 522(e) applied to subsidence.
Id. at 98. The court found that the references in the reports to "surface effects" of underground coal mining, and "surface impacts" of underground coal mining must include subsidence. See Citizens Coal, 193 F.Supp.2d at 163-64. Finally, CCC contends that the House report also supports its position in a discussion entitled "Surface Impacts of Underground Mines," stating:
H.R.REP. No. 95-218, at 125-26 (1977). Essentially, the CCC interprets the legislative history's use of the phrase "surface impacts" which appears in 701(28) to necessarily include subsidence.
The Secretary counters with the argument that the legislative history does show that Congress had an intention to regulate subsidence within the SMCRA, but intended
H.R.REP. No. 95-218, at 126 (1977). The Secretary reiterates that Congress did not discuss subsidence as being among the "impacts" of underground mining that are prohibited in section 522(e) areas. The Secretary also noted that she had concluded during the promulgation of the regulation at issue that the passage from the Senate report on which the District Court specifically relied was "imprecise" and of questionable precedential value because it states that exploration activities are included in the definition of "surface coal mining operations" even though the statute expressly provides to the contrary. See 64 Fed.Reg. 70,844-45 (citing 30 U.S.C. § 1291(28)(A)). Furthermore, the Secretary points out that the Senate report on section 522(e) notes that "surface coal mining" is prohibited within the specified distances of public roads, occupied buildings, and active underground mines "for reasons of public health and safety." S.REP. No. 95-128, at 55. The Secretary posits that to accomplish that purpose, 522(e) need not prohibit subsidence, because underground mines must already meet the requirements of section 516, which prevents almost all risks to public health and safety.
Taken together, as is so often the case, legislative history on which both parties rely is at best inconclusive as to either interpretation. As Judge Leventhal once observed, reviewing legislative history is like "looking over a crowd and picking out your friends." Patricia M. Wald, Some Observations on the Use of Legislative History in the 1981 Supreme Court Term, 68 IOWA L. REV. 195, 214 (1983). This inconclusiveness underscores our conclusion that the statute is ambiguous on the question of whether subsidence is included within the prohibitions in 522(e). In addition, one amendment to the statute since its promulgation bolsters the reasonableness of the Secretary's interpretation. In 1992, Congress added section 720 to the SMCRA, an amendment entitled "Subsidence," which provides compensation for property owners who suffer material damage caused by subsidence to "occupied residential dwelling and structures related thereto, or non-commercial building due to underground coal mining operations." 30 U.S.C. § 1309a(a)(1). Intervenor NMA argues that the passage of this section demonstrates that Congress was aware that SMCRA does not prohibit subsidence in section 522(e) areas and therefore added the section to provide a remedy for property owners damaged by this result of an
Finally, we do not find compelling the argument drawn by CCC from a footnote in the District Court's opinion. At the end of its opinion, the court added the note, which reads in pertinent part: "[s]ection  also falls within § [516(d)]'s mandate that SMCRA provisions `relating to State and Federal programs [and] permits ... shall be applicable to surface operations and surface impacts incident to an underground coal mine,' since it imposes requirements on federal and state regulators...." Citizens Coal, 193 F.Supp.2d at 165 n. 3. The District Court offered no further reasoning or explanation in support of this conclusion. CCC argues that this footnote is an alternative holding meaning that section 516(d), by referencing provisions "relating to ... permits" unambiguously requires the Secretary to apply section 522(e) to protect against subsidence, simply because of the use of the word "permitted" in that later section. We disagree.
There is certainly a colorable difference between the noun "permit" and the verb "permitted." The SMCRA contains a number of provisions which do deal directly and specifically with "Permits." For example, section 506, 30 U.S.C. § 1256, is entitled "Permits" and provides for the terms, termination, and renewal of permits. The following section 30 U.S.C. § 1257 is entitled "Application requirements" and provides for the fee and content requirements of the permits. These sections stand in contrast to section 522(e) which provides for a number of prohibitions, and uses the verb "permitted" simply to describe the geographical limitations to which the Secretary is bound when "[d]esignating areas unsuitable for surface coal mining," as the title of the section instructs. See 30 U.S.C. § 1272(e) (no surface coal mining operations ... shall be permitted — (1) on any lands within the boundaries of units of the National Park System ... (2) on any Federal lands within the boundaries of any national forest ... (3) which will adversely affect any publicly owned park ... (4) within 100 feet of the outside right-of-way line of any public road ... (5) within 300 feet from any occupied dwelling....). Thus, the "permit" argument based on section 516(d) has no compelling force on the interpretation of section 522(e).
For the reasons explained above, we find that the definition of "surface coal mining operations" in SMCRA section 701(28) is ambiguous as to whether Congress intended it to include subsidence, and therefore, whether subsidence is among the prohibitions contained in section 522(e) is likewise ambiguous. We conclude that the Secretary's interpretation, albeit perhaps not the "most natural" reading, is a reasonable one, and therefore we defer to that interpretation in accordance